diff --git a/common/sudo_conf.c b/common/sudo_conf.c
index 73dc73aa1..bde2c3384 100644
--- a/common/sudo_conf.c
+++ b/common/sudo_conf.c
@@ -182,16 +182,14 @@ set_var_group_source(const char *entry, const char *conf_file)
 static void
 set_var_max_groups(const char *entry, const char *conf_file)
 {
-    long lval;
-    char *ep;
+    int max_groups;
 
-    lval = strtol(entry, &ep, 10);
-    if (*entry == '\0' || *ep != '\0' || lval <= 0 || lval > INT_MAX ||
-	(errno == ERANGE && lval == LONG_MAX)) {
-	warningx(U_("invalid max groups `%s' in %s, line %d"), entry,
-		    conf_file, conf_lineno);
+    max_groups = strtonum(entry, 1, INT_MAX, NULL);
+    if (max_groups > 0) {
+	sudo_conf_data.max_groups = max_groups;
     } else {
-	sudo_conf_data.max_groups = (int)lval;
+	warningx(U_("invalid max groups `%s' in %s, line %d"), entry,
+	    conf_file, conf_lineno);
     }
 }
 
diff --git a/common/ttysize.c b/common/ttysize.c
index c30643d58..13c5b5779 100644
--- a/common/ttysize.c
+++ b/common/ttysize.c
@@ -77,10 +77,14 @@ get_ttysize(int *rowp, int *colp)
 	char *p;
 
 	/* Fall back on $LINES and $COLUMNS. */
-	if ((p = getenv("LINES")) == NULL || (*rowp = atoi(p)) <= 0)
+	if ((p = getenv("LINES")) == NULL ||
+	    (*rowp = strtonum(p, 1, INT_MAX, NULL)) <= 0) {
 	    *rowp = 24;
-	if ((p = getenv("COLUMNS")) == NULL || (*colp = atoi(p)) <= 0)
+	}
+	if ((p = getenv("COLUMNS")) == NULL ||
+	    (*colp = strtonum(p, 1, INT_MAX, NULL)) <= 0) {
 	    *colp = 80;
+	}
     }
 
     debug_return;
diff --git a/compat/Makefile.in b/compat/Makefile.in
index 874854b1e..843200e38 100644
--- a/compat/Makefile.in
+++ b/compat/Makefile.in
@@ -222,7 +222,8 @@ strlcpy.lo: $(srcdir)/strlcpy.c $(incdir)/missing.h $(top_builddir)/config.h
 strsignal.lo: $(srcdir)/strsignal.c $(incdir)/gettext.h $(incdir)/missing.h \
               $(top_builddir)/config.h
 	$(LIBTOOL) --mode=compile $(CC) -c -o $@ $(CPPFLAGS) $(CFLAGS) $(PIE_CFLAGS) $(SSP_CFLAGS) $(DEFS) $(srcdir)/strsignal.c
-strtonum.lo: $(srcdir)/strtonum.c $(incdir)/missing.h $(top_builddir)/config.h
+strtonum.lo: $(srcdir)/strtonum.c $(incdir)/gettext.h $(incdir)/missing.h \
+             $(top_builddir)/config.h
 	$(LIBTOOL) --mode=compile $(CC) -c -o $@ $(CPPFLAGS) $(CFLAGS) $(PIE_CFLAGS) $(SSP_CFLAGS) $(DEFS) $(srcdir)/strtonum.c
 utimes.lo: $(srcdir)/utimes.c $(incdir)/missing.h $(top_builddir)/config.h \
            $(top_srcdir)/compat/utime.h
diff --git a/compat/closefrom.c b/compat/closefrom.c
index da2870a46..c2fe77735 100644
--- a/compat/closefrom.c
+++ b/compat/closefrom.c
@@ -86,7 +86,7 @@ closefrom_fallback(int lowfd)
     for (fd = lowfd; fd < maxfd; fd++) {
 #ifdef __APPLE__
 	/* Avoid potential crash with libdispatch when we close its fds. */
-	(void) fcntl(fd, F_SETFD, FD_CLOEXEC);
+	(void) fcntl((int) fd, F_SETFD, FD_CLOEXEC);
 #else
 	(void) close((int) fd);
 #endif
@@ -123,17 +123,17 @@ void
 closefrom(int lowfd)
 {
     struct dirent *dent;
+    const char *errstr;
     DIR *dirp;
-    char *endp;
-    long fd;
+    int fd;
 
     /* Use /proc/self/fd directory if it exists. */
     if ((dirp = opendir("/proc/self/fd")) != NULL) {
 	while ((dent = readdir(dirp)) != NULL) {
-	    fd = strtol(dent->d_name, &endp, 10);
-	    if (dent->d_name != endp && *endp == '\0' &&
-		fd >= 0 && fd < INT_MAX && fd >= lowfd && fd != dirfd(dirp))
-		(void) close((int) fd);
+	    fd = strtonum(dent->d_name, lowfd, INT_MAX, &errstr);
+	    if (errstr == NULL && fd != dirfd(dirp)) {
+		(void) close(fd);
+	    }
 	}
 	(void) closedir(dirp);
     } else
diff --git a/compat/getaddrinfo.c b/compat/getaddrinfo.c
index ef514b5bc..2e3da84c5 100644
--- a/compat/getaddrinfo.c
+++ b/compat/getaddrinfo.c
@@ -187,29 +187,6 @@ freeaddrinfo(struct addrinfo *ai)
 }
 
 
-/*
- * Convert a numeric service string to a number with error checking, returning
- * true if the number was parsed correctly and false otherwise.  Stores the
- * converted number in the second argument.  Equivalent to calling strtol, but
- * with the base always fixed at 10, with checking of errno, ensuring that all
- * of the string is consumed, and checking that the resulting number is
- * positive.
- */
-static int
-convert_service(const char *string, long *result)
-{
-    char *end;
-
-    if (*string == '\0')
-        return 0;
-    errno = 0;
-    *result = strtol(string, &end, 10);
-    if (errno != 0 || *end != '\0' || *result < 0)
-        return 0;
-    return 1;
-}
-
-
 /*
  * Allocate a new addrinfo struct, setting some defaults given that this
  * implementation is IPv4 only.  Also allocates an attached sockaddr_in and
@@ -268,12 +245,14 @@ gai_service(const char *servname, int flags, int *type, unsigned short *port)
 {
     struct servent *servent;
     const char *protocol;
-    long value;
+    const char *errstr;
+    unsigned short value;
 
-    if (convert_service(servname, &value)) {
-        if (value > (1L << 16) - 1)
-            return EAI_SERVICE;
+    value = strtonum(servname, 0, USHRT_MAX, &errstr);
+    if (errstr == NULL) {
         *port = value;
+    } else if (errno == ERANGE) {
+	return EAI_SERVICE;
     } else {
         if (flags & AI_NUMERICSERV)
             return EAI_NONAME;
diff --git a/compat/strtonum.c b/compat/strtonum.c
index d1b5e9180..7db673e28 100644
--- a/compat/strtonum.c
+++ b/compat/strtonum.c
@@ -28,6 +28,9 @@
 
 #include "missing.h"
 
+#define DEFAULT_TEXT_DOMAIN	"sudo"
+#include "gettext.h"
+
 enum strtonum_err {
     STN_VALID,
     STN_INVALID,
@@ -133,19 +136,19 @@ done:
 	result = 0;
 	errno = EINVAL;
 	if (errstrp != NULL)
-	    *errstrp = "invalid";
+	    *errstrp = N_("invalid");
 	break;
     case STN_TOOSMALL:
 	result = 0;
 	errno = ERANGE;
 	if (errstrp != NULL)
-	    *errstrp = "too small";
+	    *errstrp = N_("too small");
 	break;
     case STN_TOOBIG:
 	result = 0;
 	errno = ERANGE;
 	if (errstrp != NULL)
-	    *errstrp = "too large";
+	    *errstrp = N_("too large");
 	break;
     }
     return result;
diff --git a/configure b/configure
index f37737f86..35d91eb54 100755
--- a/configure
+++ b/configure
@@ -16297,7 +16297,7 @@ $as_echo "#define HAVE_LONG_LONG_INT 1" >>confdefs.h
   fi
 
 if test X"$ac_cv_type_long_long_int" != X"yes"; then
-    as_fn_error $? "\"C compiler does not appear have required long long support\"" "$LINENO" 5
+    as_fn_error $? "\"C compiler does not appear to support the long long int type\"" "$LINENO" 5
 fi
 # The cast to long int works around a bug in the HP C Compiler
 # version HP92453-01 B.11.11.23709.GP, which incorrectly rejects
diff --git a/configure.ac b/configure.ac
index c5bf464e8..5f11b943b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2196,7 +2196,7 @@ AC_CHECK_TYPES([struct in6_addr], [], [], [#include <sys/types.h>
 #include <netinet/in.h>])
 AC_TYPE_LONG_LONG_INT
 if test X"$ac_cv_type_long_long_int" != X"yes"; then
-    AC_MSG_ERROR(["C compiler does not appear have required long long support"])
+    AC_MSG_ERROR(["C compiler does not appear to support the long long int type"])
 fi
 AC_CHECK_SIZEOF([long int])
 AC_CHECK_TYPE(id_t, unsigned int)
diff --git a/include/missing.h b/include/missing.h
index a4051b3ad..6dfceead1 100644
--- a/include/missing.h
+++ b/include/missing.h
@@ -124,10 +124,38 @@
 # define OPEN_MAX	256
 #endif
 
+#ifndef USHRT_MAX
+# define USHRT_MAX	0xffff
+#endif
+
 #ifndef INT_MAX
 # define INT_MAX	0x7fffffff
 #endif
 
+#ifndef INT_MIN
+# define INT_MIN	(-0x7fffffff-1)
+#endif
+
+#ifndef UINT_MAX
+# define UINT_MAX	0xffffffffU
+#endif
+
+#ifndef LLONG_MAX
+# if defined(QUAD_MAX)
+#  define LLONG_MAX	QUAD_MAX
+# else
+#  define LLONG_MAX	0x7fffffffffffffffLL
+# endif
+#endif
+
+#ifndef LLONG_MIN
+# if defined(QUAD_MIN)
+#  define LLONG_MIN	QUAD_MIN
+# else
+#  define LLONG_MIN	(-0x7fffffffffffffffLL-1)
+# endif
+#endif
+
 #ifndef PATH_MAX
 # ifdef _POSIX_PATH_MAX
 #  define PATH_MAX		_POSIX_PATH_MAX
diff --git a/plugins/sudoers/boottime.c b/plugins/sudoers/boottime.c
index 68672c0f8..16fb376f0 100644
--- a/plugins/sudoers/boottime.c
+++ b/plugins/sudoers/boottime.c
@@ -74,21 +74,12 @@ get_boottime(struct timeval *tv)
     if (fp != NULL) {
 	while ((len = getline(&line, &linesize, fp)) != -1) {
 	    if (strncmp(line, "btime ", 6) == 0) {
-#ifdef HAVE_STRTOLL
-		long long llval = strtoll(line + 6, &ep, 10);
-		if (line[6] != '\0' && *ep == '\0' && (time_t)llval == llval) {
+		long long llval = strtonum(line + 6, 1, LLONG_MAX, NULL);
+		if (llval > 0) {
 		    tv->tv_sec = (time_t)llval;
 		    tv->tv_usec = 0;
 		    debug_return_bool(1);
 		}
-#else
-		long lval = strtol(line + 6, &ep, 10);
-		if (line[6] != '\0' && *ep == '\0' && (time_t)lval == lval) {
-		    tv->tv_sec = (time_t)llval;
-		    tv->tv_usec = 0;
-		    debug_return_bool(1);
-		}
-#endif
 	    }
 	}
 	fclose(fp);
diff --git a/plugins/sudoers/defaults.c b/plugins/sudoers/defaults.c
index 2e0ec7ab6..b6f7622c5 100644
--- a/plugins/sudoers/defaults.c
+++ b/plugins/sudoers/defaults.c
@@ -600,18 +600,20 @@ check_defaults(int what, bool quiet)
 static bool
 store_int(char *val, struct sudo_defs_types *def, int op)
 {
-    char *endp;
-    long l;
+    const char *errstr;
+    int i;
     debug_decl(store_int, SUDO_DEBUG_DEFAULTS)
 
     if (op == false) {
 	def->sd_un.ival = 0;
     } else {
-	l = strtol(val, &endp, 10);
-	if (*endp != '\0')
+	i = strtonum(val, INT_MIN, INT_MAX, &errstr);
+	if (errstr != NULL) {
+	    sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_LINENO,
+		"%s is %s", val, errstr);
 	    debug_return_bool(false);
-	/* XXX - should check against INT_MAX */
-	def->sd_un.ival = (int)l;
+	}
+	def->sd_un.ival = i;
     }
     if (def->callback)
 	debug_return_bool(def->callback(val));
@@ -621,18 +623,21 @@ store_int(char *val, struct sudo_defs_types *def, int op)
 static bool
 store_uint(char *val, struct sudo_defs_types *def, int op)
 {
-    char *endp;
-    long l;
+    const char *errstr;
+    unsigned int u;
     debug_decl(store_uint, SUDO_DEBUG_DEFAULTS)
 
     if (op == false) {
 	def->sd_un.ival = 0;
     } else {
-	l = strtol(val, &endp, 10);
-	if (*endp != '\0' || l < 0)
+	u = strtonum(val, 0, UINT_MAX, &errstr);
+	if (errstr != NULL) {
+	    sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_LINENO,
+		"%s is %s", val, errstr);
 	    debug_return_bool(false);
-	/* XXX - should check against INT_MAX */
-	def->sd_un.ival = (unsigned int)l;
+	}
+	/* XXX - should have uival */
+	def->sd_un.ival = u;
     }
     if (def->callback)
 	debug_return_bool(def->callback(val));
@@ -814,7 +819,7 @@ store_mode(char *val, struct sudo_defs_types *def, int op)
 	def->sd_un.mode = (mode_t)0777;
     } else {
 	l = strtol(val, &endp, 8);
-	if (*endp != '\0' || l < 0 || l > 0777)
+	if (endp == val || *endp != '\0' || l < 0 || l > 0777)
 	    debug_return_bool(false);
 	def->sd_un.mode = (mode_t)l;
     }
diff --git a/plugins/sudoers/iolog.c b/plugins/sudoers/iolog.c
index 133218050..0b4ea23bb 100644
--- a/plugins/sudoers/iolog.c
+++ b/plugins/sudoers/iolog.c
@@ -136,17 +136,22 @@ io_mkdirs(char *path, mode_t mode, bool is_temp)
 int
 io_set_max_sessid(const char *maxval)
 {
-    unsigned long ulval;
-    char *ep;
+    const char *errstr;
+    unsigned int value;
+    debug_decl(io_set_max_sessid, SUDO_DEBUG_UTIL)
 
-    errno = 0;
-    ulval = strtoul(maxval, &ep, 0);
-    if (*maxval != '\0' && *ep == '\0' &&
-	(errno != ERANGE || ulval != ULONG_MAX)) {
-	sessid_max = MIN((unsigned int)ulval, SESSID_MAX);
-	return true;
+    value = strtonum(maxval, 0, SESSID_MAX, &errstr);
+    if (errstr != NULL) {
+	if (errno != ERANGE) {
+	    sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_LINENO,
+		"bad maxseq: %s is %s", maxval, errstr);
+	    debug_return_bool(false);
+	}
+	/* Out of range, clamp to SESSID_MAX as documented. */
+	value = SESSID_MAX;
     }
-    return false;
+    sessid_max = value;
+    debug_return_bool(true);
 }
 
 /*
@@ -202,7 +207,7 @@ io_nextid(char *iolog_dir, char *iolog_dir_fallback, char sessid[7])
 		nread = read(fd2, buf, sizeof(buf));
 		if (nread > 0) {
 		    id = strtoul(buf, &ep, 36);
-		    if (buf == ep || id >= sessid_max)
+		    if (ep == buf || *ep != '\0' || id >= sessid_max)
 			id = 0;
 		}
 		close(fd2);
@@ -217,7 +222,7 @@ io_nextid(char *iolog_dir, char *iolog_dir_fallback, char sessid[7])
 	    if (nread == -1)
 		log_fatal(USE_ERRNO, N_("unable to read %s"), pathbuf);
 	    id = strtoul(buf, &ep, 36);
-	    if (buf == ep || id >= sessid_max)
+	    if (ep == buf || *ep != '\0' || id >= sessid_max)
 		id = 0;
 	}
     }
@@ -237,7 +242,7 @@ io_nextid(char *iolog_dir, char *iolog_dir_fallback, char sessid[7])
     memcpy(sessid, buf, 6);
     sessid[6] = '\0';
 
-    /* Rewind and overwrite old seq file. */
+    /* Rewind and overwrite old seq file, including the NUL byte. */
     if (lseek(fd, (off_t)0, SEEK_SET) == (off_t)-1 || write(fd, buf, 7) != 7)
 	log_fatal(USE_ERRNO, N_("unable to write to %s"), pathbuf);
     close(fd);
@@ -332,7 +337,9 @@ iolog_deserialize_info(struct iolog_details *details, char * const user_info[],
 	switch (**cur) {
 	case 'c':
 	    if (strncmp(*cur, "cols=", sizeof("cols=") - 1) == 0) {
-		details->cols = atoi(*cur + sizeof("cols=") - 1);
+		int n = strtonum(*cur + sizeof("cols=") - 1, 1, INT_MAX, NULL);
+		if (n > 0)
+		    details->cols = n;
 		continue;
 	    }
 	    if (strncmp(*cur, "cwd=", sizeof("cwd=") - 1) == 0) {
@@ -342,7 +349,9 @@ iolog_deserialize_info(struct iolog_details *details, char * const user_info[],
 	    break;
 	case 'l':
 	    if (strncmp(*cur, "lines=", sizeof("lines=") - 1) == 0) {
-		details->lines = atoi(*cur + sizeof("lines=") - 1);
+		int n = strtonum(*cur + sizeof("lines=") - 1, 1, INT_MAX, NULL);
+		if (n > 0)
+		    details->lines = n;
 		continue;
 	    }
 	    break;
diff --git a/plugins/sudoers/ldap.c b/plugins/sudoers/ldap.c
index 4e5e69f70..82ad6c3e9 100644
--- a/plugins/sudoers/ldap.c
+++ b/plugins/sudoers/ldap.c
@@ -1398,6 +1398,7 @@ sudo_ldap_parse_keyword(const char *keyword, const char *value,
     struct ldap_config_table *table)
 {
     struct ldap_config_table *cur;
+    const char *errstr;
     debug_decl(sudo_ldap_parse_keyword, SUDO_DEBUG_LDAP)
 
     /* Look up keyword in config tables */
@@ -1418,7 +1419,11 @@ sudo_ldap_parse_keyword(const char *keyword, const char *value,
 		*(int *)(cur->valp) = atobool(value) == true;
 		break;
 	    case CONF_INT:
-		*(int *)(cur->valp) = atoi(value);
+		*(int *)(cur->valp) = strtonum(value, INT_MIN, INT_MAX, &errstr);
+		if (errstr != NULL) {
+		    warningx(U_("%s: %s: value %s out of range)"),
+			path_ldap_conf, keyword, value);
+		}
 		break;
 	    case CONF_STR:
 		efree(*(char **)(cur->valp));
diff --git a/plugins/sudoers/match_addr.c b/plugins/sudoers/match_addr.c
index 620394e55..f3995f390 100644
--- a/plugins/sudoers/match_addr.c
+++ b/plugins/sudoers/match_addr.c
@@ -109,6 +109,7 @@ addr_matches_if_netmask(const char *n, const char *m)
     unsigned int j;
 #endif
     unsigned int family;
+    const char *errstr;
     debug_decl(addr_matches_if, SUDO_DEBUG_MATCH)
 
 #ifdef HAVE_STRUCT_IN6_ADDR
@@ -125,7 +126,12 @@ addr_matches_if_netmask(const char *n, const char *m)
 	if (strchr(m, '.')) {
 	    mask.ip4.s_addr = inet_addr(m);
 	} else {
-	    i = atoi(m);
+	    i = strtonum(m, 0, 32, &errstr);
+	    if (errstr != NULL) {
+		sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_LINENO,
+		    "IPv4 netmask %s: %s", m, errstr);
+		debug_return_bool(false);
+	    }
 	    if (i == 0)
 		mask.ip4.s_addr = 0;
 	    else if (i == 32)
@@ -139,7 +145,12 @@ addr_matches_if_netmask(const char *n, const char *m)
 #ifdef HAVE_STRUCT_IN6_ADDR
     else {
 	if (inet_pton(AF_INET6, m, &mask.ip6) <= 0) {
-	    j = atoi(m);
+	    j = strtonum(m, 0, 128, &errstr);
+	    if (errstr != NULL) {
+		sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_LINENO,
+		    "IPv6 netmask %s: %s", m, errstr);
+		debug_return_bool(false);
+	    }
 	    for (i = 0; i < sizeof(addr.ip6.s6_addr); i++) {
 		if (j < i * 8)
 		    mask.ip6.s6_addr[i] = 0;
diff --git a/plugins/sudoers/policy.c b/plugins/sudoers/policy.c
index 6c9286ede..0824abac7 100644
--- a/plugins/sudoers/policy.c
+++ b/plugins/sudoers/policy.c
@@ -91,7 +91,6 @@ sudoers_policy_deserialize_info(void *v, char **runas_user, char **runas_group)
     const char *debug_flags = NULL;
     const char *remhost = NULL;
     int flags = 0;
-    long lval;
     char *ep;
     debug_decl(sudoers_policy_deserialize_info, SUDO_DEBUG_PLUGIN)
 
@@ -119,14 +118,16 @@ sudoers_policy_deserialize_info(void *v, char **runas_user, char **runas_group)
 		continue;
 	    }
 	    if (MATCHES(*cur, "sudoers_mode=")) {
+		long lval;
 		errno = 0;
 		p = *cur + sizeof("sudoers_mode=") - 1;
 		lval = strtol(p, &ep, 8);
-		if (*p == '\0' || *ep != '\0')
-		    fatalx(U_("%s: %s"), *cur, U_("invalid value"));
-		if ((errno == ERANGE && (lval == LONG_MAX || lval == LONG_MIN))
-		    || (lval > 0777 || lval < 0))
-		    fatalx(U_("%s: %s"), *cur, U_("value out of range"));
+		if (ep == p || *ep != '\0')
+		    fatalx(U_("%s: %s"), *cur, U_("invalid"));
+		if (lval < 0)
+		    fatalx(U_("%s: %s"), *cur, U_("too small"));
+		if (lval > 0777)
+		    fatalx(U_("%s: %s"), *cur, U_("too large"));
 		sudoers_mode = (mode_t) lval;
 		continue;
 	    }
@@ -147,13 +148,9 @@ sudoers_policy_deserialize_info(void *v, char **runas_user, char **runas_group)
 	if (MATCHES(*cur, "closefrom=")) {
 	    errno = 0;
 	    p = *cur + sizeof("closefrom=") - 1;
-	    lval = strtol(p, &ep, 10);
-	    if (*p == '\0' || *ep != '\0')
-		fatalx(U_("%s: %s"), *cur, U_("invalid value"));
-	    if ((errno == ERANGE && (lval == LONG_MAX || lval == LONG_MIN))
-		|| (lval > INT_MAX || lval < 3))
-		fatalx(U_("%s: %s"), *cur, U_("value out of range"));
-	    user_closefrom = (int) lval;
+	    user_closefrom = strtonum(p, 4, INT_MAX, &errstr);
+	    if (user_closefrom == 0)
+		fatalx(U_("%s: %s"), *cur, U_(errstr));
 	    continue;
 	}
 	if (MATCHES(*cur, "debug_flags=")) {
@@ -265,13 +262,9 @@ sudoers_policy_deserialize_info(void *v, char **runas_user, char **runas_group)
 	if (MATCHES(*cur, "max_groups=")) {
 	    errno = 0;
 	    p = *cur + sizeof("max_groups=") - 1;
-	    lval = strtol(p, &ep, 10);
-	    if (*p == '\0' || *ep != '\0')
-		fatalx(U_("%s: %s"), *cur, U_("invalid value"));
-	    if ((errno == ERANGE && (lval == LONG_MAX || lval == LONG_MIN))
-		|| (lval > INT_MAX || lval <= 0))
-		fatalx(U_("%s: %s"), *cur, U_("value out of range"));
-	    sudo_user.max_groups = (int) lval;
+	    sudo_user.max_groups = strtonum(p, 1, INT_MAX, &errstr);
+	    if (sudo_user.max_groups == 0)
+		fatalx(U_("%s: %s"), *cur, U_(errstr));
 	    continue;
 	}
 	if (MATCHES(*cur, "remote_host=")) {
@@ -322,25 +315,17 @@ sudoers_policy_deserialize_info(void *v, char **runas_user, char **runas_group)
 	if (MATCHES(*cur, "lines=")) {
 	    errno = 0;
 	    p = *cur + sizeof("lines=") - 1;
-	    lval = strtol(p, &ep, 10);
-	    if (*p == '\0' || *ep != '\0')
-		fatalx(U_("%s: %s"), *cur, U_("invalid value"));
-	    if ((errno == ERANGE && (lval == LONG_MAX || lval == LONG_MIN))
-		|| (lval > INT_MAX || lval <= 0))
-		fatalx(U_("%s: %s"), *cur, U_("value out of range"));
-	    sudo_user.lines = (int) lval;
+	    sudo_user.lines = strtonum(p, 1, INT_MAX, &errstr);
+	    if (sudo_user.lines == 0)
+		fatalx(U_("%s: %s"), *cur, U_(errstr));
 	    continue;
 	}
 	if (MATCHES(*cur, "cols=")) {
 	    errno = 0;
 	    p = *cur + sizeof("cols=") - 1;
-	    lval = strtol(p, &ep, 10);
-	    if (*p == '\0' || *ep != '\0')
-		fatalx(U_("%s: %s"), *cur, U_("invalid value"));
-	    if ((errno == ERANGE && (lval == LONG_MAX || lval == LONG_MIN))
-		|| (lval > INT_MAX || lval <= 0))
-		fatalx(U_("%s: %s"), *cur, U_("value out of range"));
-	    sudo_user.cols = (int) lval;
+	    sudo_user.cols = strtonum(p, 1, INT_MAX, &errstr);
+	    if (sudo_user.lines == 0)
+		fatalx(U_("%s: %s"), *cur, U_(errstr));
 	    continue;
 	}
 	if (MATCHES(*cur, "sid=")) {
diff --git a/plugins/sudoers/regress/logging/check_wrap.c b/plugins/sudoers/regress/logging/check_wrap.c
index 3d5a8195e..056482711 100644
--- a/plugins/sudoers/regress/logging/check_wrap.c
+++ b/plugins/sudoers/regress/logging/check_wrap.c
@@ -59,6 +59,7 @@ main(int argc, char *argv[])
     size_t len;
     FILE *fp;
     char *cp, *dash, *line, lines[2][2048];
+    int lineno = 0;
     int which = 0;
 
     initprogname(argc > 0 ? argv[0] : "check_wrap");
@@ -83,13 +84,20 @@ main(int argc, char *argv[])
 
 	/* If we read the 2nd line, parse list of line lengths and check. */
 	if (which) {
+	    lineno++;
 	    for (cp = strtok(lines[1], ","); cp != NULL; cp = strtok(NULL, ",")) {
 		size_t maxlen;
 		/* May be either a number or a range. */
-		len = maxlen = atoi(cp);
 		dash = strchr(cp, '-');
-		if (dash)
-		    maxlen = atoi(dash + 1);
+		if (dash != NULL) {
+		    *dash = '\0';
+		    len = strtonum(cp, 1, INT_MAX, NULL);
+		    maxlen = strtonum(dash + 1, 1, INT_MAX, NULL);
+		} else {
+		    len = maxlen = strtonum(cp, 1, INT_MAX, NULL);
+		}
+		if (len == 0 || maxlen == 0)
+		    fatalx("%s: invalid length on line %d\n", argv[1], lineno);
 		while (len <= maxlen) {
 		    printf("# word wrap at %d characters\n", (int)len);
 		    writeln_wrap(stdout, lines[0], strlen(lines[0]), len);
diff --git a/plugins/sudoers/regress/parser/check_addr.c b/plugins/sudoers/regress/parser/check_addr.c
index 86576a2da..317f79264 100644
--- a/plugins/sudoers/regress/parser/check_addr.c
+++ b/plugins/sudoers/regress/parser/check_addr.c
@@ -54,6 +54,7 @@ static int
 check_addr(char *input)
 {
     int expected, matched;
+    const char *errstr;
     size_t len;
     char *cp;
 
@@ -65,7 +66,9 @@ check_addr(char *input)
     cp = input + len;
     while (isspace((unsigned char)*cp))
 	cp++;
-    expected = atoi(cp);
+    expected = strtonum(cp, 0, 1, &errstr);
+    if (errstr != NULL)
+	fatalx("expecting 0 or 1, got %s", cp);
     input[len] = '\0';
 
     matched = addr_matches(input);
diff --git a/plugins/sudoers/sudoreplay.c b/plugins/sudoers/sudoreplay.c
index ce752dc2d..c3537cfd1 100644
--- a/plugins/sudoers/sudoreplay.c
+++ b/plugins/sudoers/sudoreplay.c
@@ -438,6 +438,7 @@ replay_session(const double max_wait, const char *decimal)
 	bool need_nlcr = false;
 	char last_char = '\0';
 
+	buf[strcspn(buf, "\n")] = '\0';
 	if (!parse_timing(buf, decimal, &idx, &seconds, &nbytes))
 	    fatalx(U_("invalid timing file line: %s"), buf);
 
@@ -802,13 +803,9 @@ parse_logfile(char *logfile)
 {
     FILE *fp;
     char *buf = NULL, *cp, *ep;
+    const char *errstr;
     size_t bufsize = 0, cwdsize = 0, cmdsize = 0;
     struct log_info *li = NULL;
-#ifdef HAVE_STRTOLL
-    long long llval;
-#else
-    long lval;
-#endif
     debug_decl(parse_logfile, SUDO_DEBUG_UTIL)
 
     fp = fopen(logfile, "r");
@@ -837,26 +834,21 @@ parse_logfile(char *logfile)
     /*
      * Crack the log line (rows and cols not present in old versions).
      *	timestamp:user:runas_user:runas_group:tty:rows:cols
+     * XXX - probably better to use strtok and switch on the state.
      */
     buf[strcspn(buf, "\n")] = '\0';
+    cp = buf;
 
     /* timestamp */
-    errno = 0;
-#ifdef HAVE_STRTOLL
-    llval = strtoll(buf, &ep, 10);
-    if (buf[0] == '\0' || *ep != ':')
+    if ((ep = strchr(cp, ':')) == NULL)
 	goto bad;
-    if (errno == ERANGE && (llval == LLONG_MAX || llval == LLONG_MIN))
+    *ep = '\0';
+    li->tstamp = strtonum(cp, LLONG_MIN, LLONG_MAX, &errstr);
+    if (errstr != NULL) {
+	sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_LINENO,
+	    "%s: timestamp %s is %s", logfile, cp, errstr);
 	goto bad;
-    li->tstamp = (time_t)llval;
-#else
-    lval = strtol(buf, &ep, 10);
-    if (buf[0] == '\0' || *ep != ':')
-	goto bad;
-    if (errno == ERANGE && (lval == LONG_MAX || lval == LONG_MIN))
-	goto bad;
-    li->tstamp = (time_t)lval;
-#endif /* HAVE_STRTOLL */
+    }
 
     /* user */
     cp = ep + 1;
@@ -880,14 +872,28 @@ parse_logfile(char *logfile)
     /* tty, followed by optional rows + columns */
     cp = ep + 1;
     if ((ep = strchr(cp, ':')) == NULL) {
+	/* just the tty */
 	li->tty = estrdup(cp);
     } else {
+	/* tty followed by rows + columns */
 	li->tty = estrndup(cp, (size_t)(ep - cp));
 	cp = ep + 1;
-	li->rows = atoi(cp);
+	/* need to NULL out separator to use strtonum() */
 	if ((ep = strchr(cp, ':')) != NULL) {
+	    *ep = '\0';
+	}
+	li->rows = strtonum(cp, 1, INT_MAX, &errstr);
+	if (errstr != NULL) {
+	    sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_LINENO,
+		"%s: tty rows %s is %s", logfile, cp, errstr);
+	}
+	if (ep != NULL) {
 	    cp = ep + 1;
-	    li->cols = atoi(cp);
+	    li->cols = strtonum(cp, 1, INT_MAX, &errstr);
+	    if (errstr != NULL) {
+		sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_LINENO,
+		    "%s: tty cols %s is %s", logfile, cp, errstr);
+	    }
 	}
     }
     fclose(fp);
@@ -1158,6 +1164,8 @@ parse_timing(const char *buf, const char *decimal, int *idx, double *seconds,
 
     /* Parse index */
     ul = strtoul(buf, &ep, 10);
+    if (ep == buf || !isspace((unsigned char) *ep))
+	goto bad;
     if (ul >= IOFD_TIMING) {
 	if (ul != 6)
 	    goto bad;
@@ -1176,11 +1184,10 @@ parse_timing(const char *buf, const char *decimal, int *idx, double *seconds,
      */
     errno = 0;
     l = strtol(cp, &ep, 10);
-    if ((errno == ERANGE && (l == LONG_MAX || l == LONG_MIN)) ||
-	l < 0 || l > INT_MAX ||
-	(*ep != '.' && strncmp(ep, decimal, strlen(decimal)) != 0)) {
+    if (ep == cp || (*ep != '.' && strncmp(ep, decimal, strlen(decimal)) != 0))
+	goto bad;
+    if (l < 0 || l > INT_MAX || (errno == ERANGE && l == LONG_MAX))
 	goto bad;
-    }
     *seconds = (double)l;
     cp = ep + (*ep == '.' ? 1 : strlen(decimal));
     d = 10.0;
@@ -1195,7 +1202,7 @@ parse_timing(const char *buf, const char *decimal, int *idx, double *seconds,
 
     errno = 0;
     ul = strtoul(cp, &ep, 10);
-    if (errno == ERANGE && ul == ULONG_MAX)
+    if (ep == cp || *ep != '\0' || (errno == ERANGE && ul == ULONG_MAX))
 	goto bad;
     *nbytes = (size_t)ul;
 
diff --git a/plugins/system_group/system_group.c b/plugins/system_group/system_group.c
index f53374ccc..c0cd563b0 100644
--- a/plugins/system_group/system_group.c
+++ b/plugins/system_group/system_group.c
@@ -73,6 +73,8 @@ static sysgroup_getgrgid_t sysgroup_getgrgid;
 static sysgroup_gr_delref_t sysgroup_gr_delref;
 static bool need_setent;
 
+extern id_t atoid(const char *str, const char *sep, char **endp, const char **errstr);
+
 static int
 sysgroup_init(int version, sudo_printf_t sudo_printf, char *const argv[])
 {
@@ -128,16 +130,15 @@ sysgroup_cleanup(void)
 static int
 sysgroup_query(const char *user, const char *group, const struct passwd *pwd)
 {
-    char **member, *ep = '\0';
+    char **member;
     struct group *grp;
 
     grp = sysgroup_getgrnam(group);
     if (grp == NULL && group[0] == '#' && group[1] != '\0') {
-	long lval = strtol(group + 1, &ep, 10);
-	if (*ep == '\0') {
-	    if ((lval != LONG_MAX && lval != LONG_MIN) || errno != ERANGE)
-		grp = sysgroup_getgrgid((gid_t)lval);
-	}
+	const char *errstr;
+	gid_t gid = atoid(group + 1, NULL, NULL, &errstr);
+	if (errstr == NULL)
+	    grp = sysgroup_getgrgid(gid);
     }
     if (grp != NULL) {
 	for (member = grp->gr_mem; *member != NULL; member++) {
diff --git a/src/parse_args.c b/src/parse_args.c
index 61d4647d9..99fb249f2 100644
--- a/src/parse_args.c
+++ b/src/parse_args.c
@@ -178,7 +178,7 @@ parse_args(int argc, char **argv, int *nargc, char ***nargv, char ***settingsp,
     char *cp, **env_add, **settings;
     const char *runas_user = NULL;
     const char *runas_group = NULL;
-    const char *debug_flags;
+    const char *debug_flags, *errstr;
     int nenv = 0;
     int env_size = 32;
     debug_decl(parse_args, SUDO_DEBUG_ARGS)
@@ -242,8 +242,9 @@ parse_args(int argc, char **argv, int *nargc, char ***nargv, char ***settingsp,
 		    SET(flags, MODE_BACKGROUND);
 		    break;
 		case 'C':
-		    if (atoi(optarg) < 3) {
-			warningx(U_("the argument to -C must be a number greater than or equal to 3"));
+		    strtonum(optarg, 4, INT_MAX, &errstr);
+		    if (errstr != NULL) {
+			warningx(U_("the argument to -C was %s"), U_(errstr));
 			usage(1);
 		    }
 		    sudo_settings[ARG_CLOSEFROM].value = optarg;
diff --git a/src/sudo.c b/src/sudo.c
index 075b414a3..f8c3fab53 100644
--- a/src/sudo.c
+++ b/src/sudo.c
@@ -530,8 +530,7 @@ command_info_to_details(char * const info[], struct command_details *details)
 {
     int i;
     id_t id;
-    long lval;
-    char *cp, *ep;
+    char *cp;
     const char *errstr;
     debug_decl(command_info_to_details, SUDO_DEBUG_PCOMM)
 
@@ -553,16 +552,10 @@ command_info_to_details(char * const info[], struct command_details *details)
 		SET_STRING("command=", command)
 		SET_STRING("cwd=", cwd)
 		if (strncmp("closefrom=", info[i], sizeof("closefrom=") - 1) == 0) {
-		    errno = 0;
 		    cp = info[i] + sizeof("closefrom=") - 1;
-		    lval = strtol(cp, &ep, 10);
-		    if (*cp == '\0' || *ep != '\0')
-			fatalx(U_("%s: %s"), info[i], U_("invalid value"));
-		    if ((errno == ERANGE &&
-			(lval == LONG_MAX || lval == LONG_MIN)) ||
-			(lval > INT_MAX || lval < 0))
-			fatalx(U_("%s: %s"), info[i], U_("value out of range"));
-		    details->closefrom = (int)lval;
+		    details->closefrom = strtonum(cp, 0, INT_MAX, &errstr);
+		    if (errstr != NULL)
+			fatalx(U_("%s: %s"), cp, U_(errstr));
 		    break;
 		}
 		break;
@@ -578,16 +571,10 @@ command_info_to_details(char * const info[], struct command_details *details)
 		break;
 	    case 'n':
 		if (strncmp("nice=", info[i], sizeof("nice=") - 1) == 0) {
-		    errno = 0;
 		    cp = info[i] + sizeof("nice=") - 1;
-		    lval = strtol(cp, &ep, 10);
-		    if (*cp == '\0' || *ep != '\0')
-			fatalx(U_("%s: %s"), info[i], U_("invalid value"));
-		    if ((errno == ERANGE &&
-			(lval == LONG_MAX || lval == LONG_MIN)) ||
-			(lval > INT_MAX || lval < INT_MIN))
-			fatalx(U_("%s: %s"), info[i], U_("value out of range"));
-		    details->priority = (int)lval;
+		    details->priority = strtonum(cp, INT_MIN, INT_MAX, &errstr);
+		    if (errstr != NULL)
+			fatalx(U_("%s: %s"), cp, U_(errstr));
 		    SET(details->flags, CD_SET_PRIORITY);
 		    break;
 		}
@@ -686,31 +673,27 @@ command_info_to_details(char * const info[], struct command_details *details)
 		break;
 	    case 't':
 		if (strncmp("timeout=", info[i], sizeof("timeout=") - 1) == 0) {
-		    errno = 0;
 		    cp = info[i] + sizeof("timeout=") - 1;
-		    lval = strtol(cp, &ep, 10);
-		    if (*cp == '\0' || *ep != '\0')
-			fatalx(U_("%s: %s"), info[i], U_("invalid value"));
-		    if ((errno == ERANGE &&
-			(lval == LONG_MAX || lval == LONG_MIN)) ||
-			(lval > INT_MAX || lval < 0))
-			fatalx(U_("%s: %s"), info[i], U_("value out of range"));
-		    details->timeout = (int)lval;
+		    details->timeout = strtonum(cp, 0, INT_MAX, &errstr);
+		    if (errstr != NULL)
+			fatalx(U_("%s: %s"), cp, U_(errstr));
 		    SET(details->flags, CD_SET_TIMEOUT);
 		    break;
 		}
 		break;
 	    case 'u':
 		if (strncmp("umask=", info[i], sizeof("umask=") - 1) == 0) {
+		    long lval;
+		    char *ep;
 		    errno = 0;
 		    cp = info[i] + sizeof("umask=") - 1;
 		    lval = strtol(cp, &ep, 8);
-		    if (*cp == '\0' || *ep != '\0')
-			fatalx(U_("%s: %s"), info[i], U_("invalid value"));
-		    if ((errno == ERANGE &&
-			(lval == LONG_MAX || lval == LONG_MIN)) ||
-			(lval > 0777 || lval < 0))
-			fatalx(U_("%s: %s"), info[i], U_("value out of range"));
+		    if (ep == cp || *ep != '\0')
+			fatalx(U_("%s: %s"), info[i], U_("invalid"));
+		    if (lval < 0)
+			fatalx(U_("%s: %s"), info[i], U_("too small"));
+		    if (lval > 0777)
+			fatalx(U_("%s: %s"), info[i], U_("too large"));
 		    details->umask = (mode_t)lval;
 		    SET(details->flags, CD_SET_UMASK);
 		    break;
diff --git a/src/ttyname.c b/src/ttyname.c
index 6551b7cc5..b9532e15d 100644
--- a/src/ttyname.c
+++ b/src/ttyname.c
@@ -441,11 +441,16 @@ get_process_ttyname(void)
 	if (len != -1) {
 	    /* Field 7 is the tty dev (0 if no tty) */
 	    char *cp = line;
+	    const char *errstr;
 	    int field = 1;
 	    while (*cp != '\0') {
 		if (*cp++ == ' ') {
 		    if (++field == 7) {
-			dev_t tdev = (dev_t)atoi(cp);
+			dev_t tdev = strtonum(cp, INT_MIN, INT_MAX, &errstr);
+			if (errstr) {
+			    sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_LINENO,
+				"%s: tty device number %s", path, errstr);
+			}
 			if (tdev > 0)
 			    tty = sudo_ttyname_dev(tdev);
 			break;