diff --git a/plugins/sudoers/iolog.c b/plugins/sudoers/iolog.c
index 1782d4f54..3047a0338 100644
--- a/plugins/sudoers/iolog.c
+++ b/plugins/sudoers/iolog.c
@@ -135,7 +135,7 @@ mkdir_parents(char *path)
  * Uses file locking to avoid sequence number collisions.
  */
 void
-io_nextid(char *iolog_dir, char sessid[7])
+io_nextid(char *iolog_dir, char *iolog_dir_fallback, char sessid[7])
 {
     struct stat sb;
     char buf[32], *ep;
@@ -172,14 +172,41 @@ io_nextid(char *iolog_dir, char sessid[7])
 	log_fatal(USE_ERRNO, _("unable to open %s"), pathbuf);
     lock_file(fd, SUDO_LOCK);
 
-    /* Read seq number (base 36). */
-    nread = read(fd, buf, sizeof(buf));
-    if (nread != 0) {
-	if (nread == -1)
-	    log_fatal(USE_ERRNO, _("unable to read %s"), pathbuf);
-	id = strtoul(buf, &ep, 36);
-	if (buf == ep || id >= SESSID_MAX)
-	    log_fatal(0, _("invalid sequence number %s"), pathbuf);
+    /*
+     * If there is no seq file in iolog_dir and a fallback dir was
+     * specified, look for seq in the fallback dir.  This is to work
+     * around a bug in sudo 1.8.5 and older where iolog_dir was not
+     * expanded before the sequence number was updated.
+     */
+    if (iolog_dir_fallback != NULL && fstat(fd, &sb) == 0 && sb.st_size == 0) {
+	char fallback[PATH_MAX];
+
+	len = snprintf(fallback, sizeof(fallback), "%s/seq",
+	    iolog_dir_fallback);
+	if (len > 0 && len < sizeof(fallback)) {
+	    int fd2 = open(fallback, O_RDWR|O_CREAT, S_IRUSR|S_IWUSR);
+	    if (fd2 != -1) {
+		nread = read(fd2, buf, sizeof(buf));
+		if (nread > 0) {
+		    id = strtoul(buf, &ep, 36);
+		    if (buf == ep || id >= SESSID_MAX)
+			id = 0;
+		}
+		close(fd2);
+	    }
+	}
+    }
+
+    /* Read current seq number (base 36). */
+    if (id == 0) {
+	nread = read(fd, buf, sizeof(buf));
+	if (nread != 0) {
+	    if (nread == -1)
+		log_fatal(USE_ERRNO, _("unable to read %s"), pathbuf);
+	    id = strtoul(buf, &ep, 36);
+	    if (buf == ep || id >= SESSID_MAX)
+		log_fatal(0, _("invalid sequence number %s"), pathbuf);
+	}
     }
     id++;
 
@@ -476,7 +503,7 @@ sudoers_io_open(unsigned int version, sudo_conv_t conversation,
 	/* Get next session ID and convert it into a path. */
 	tofree = emalloc(sizeof(_PATH_SUDO_IO_LOGDIR) + sizeof(sessid) + 2);
 	memcpy(tofree, _PATH_SUDO_IO_LOGDIR, sizeof(_PATH_SUDO_IO_LOGDIR));
-	io_nextid(tofree, sessid);
+	io_nextid(tofree, NULL, sessid);
 	snprintf(tofree + sizeof(_PATH_SUDO_IO_LOGDIR), sizeof(sessid) + 2,
 	    "%c%c/%c%c/%c%c", sessid[0], sessid[1], sessid[2], sessid[3],
 	    sessid[4], sessid[5]);
diff --git a/plugins/sudoers/iolog_path.c b/plugins/sudoers/iolog_path.c
index 154705d49..71030e4b5 100644
--- a/plugins/sudoers/iolog_path.c
+++ b/plugins/sudoers/iolog_path.c
@@ -46,18 +46,19 @@
 
 struct path_escape {
     const char *name;
-    size_t (*copy_fn)(char *, size_t);
+    size_t (*copy_fn)(char *, size_t, char *);
 };
 
-static size_t fill_seq(char *, size_t);
-static size_t fill_user(char *, size_t);
-static size_t fill_group(char *, size_t);
-static size_t fill_runas_user(char *, size_t);
-static size_t fill_runas_group(char *, size_t);
-static size_t fill_hostname(char *, size_t);
-static size_t fill_command(char *, size_t);
+static size_t fill_seq(char *, size_t, char *);
+static size_t fill_user(char *, size_t, char *);
+static size_t fill_group(char *, size_t, char *);
+static size_t fill_runas_user(char *, size_t, char *);
+static size_t fill_runas_group(char *, size_t, char *);
+static size_t fill_hostname(char *, size_t, char *);
+static size_t fill_command(char *, size_t, char *);
 
-static struct path_escape escapes[] = {
+/* Note: "seq" must be first in the list. */
+static struct path_escape io_path_escapes[] = {
     { "seq", fill_seq },
     { "user", fill_user },
     { "group", fill_group },
@@ -69,14 +70,14 @@ static struct path_escape escapes[] = {
 };
 
 static size_t
-fill_seq(char *str, size_t strsize)
+fill_seq(char *str, size_t strsize, char *logdir)
 {
     static char sessid[7];
     int len;
     debug_decl(sudoers_io_version, SUDO_DEBUG_UTIL)
 
     if (sessid[0] == '\0')
-	io_nextid(def_iolog_dir, sessid);
+	io_nextid(logdir, def_iolog_dir, sessid);
 
     /* Path is of the form /var/log/sudo-io/00/00/01. */
     len = snprintf(str, strsize, "%c%c/%c%c/%c%c", sessid[0],
@@ -87,14 +88,14 @@ fill_seq(char *str, size_t strsize)
 }
 
 static size_t
-fill_user(char *str, size_t strsize)
+fill_user(char *str, size_t strsize, char *unused)
 {
     debug_decl(fill_user, SUDO_DEBUG_UTIL)
     debug_return_size_t(strlcpy(str, user_name, strsize));
 }
 
 static size_t
-fill_group(char *str, size_t strsize)
+fill_group(char *str, size_t strsize, char *unused)
 {
     struct group *grp;
     size_t len;
@@ -112,14 +113,14 @@ fill_group(char *str, size_t strsize)
 }
 
 static size_t
-fill_runas_user(char *str, size_t strsize)
+fill_runas_user(char *str, size_t strsize, char *unused)
 {
     debug_decl(fill_runas_user, SUDO_DEBUG_UTIL)
     debug_return_size_t(strlcpy(str, runas_pw->pw_name, strsize));
 }
 
 static size_t
-fill_runas_group(char *str, size_t strsize)
+fill_runas_group(char *str, size_t strsize, char *unused)
 {
     struct group *grp;
     size_t len;
@@ -141,14 +142,14 @@ fill_runas_group(char *str, size_t strsize)
 }
 
 static size_t
-fill_hostname(char *str, size_t strsize)
+fill_hostname(char *str, size_t strsize, char *unused)
 {
     debug_decl(fill_hostname, SUDO_DEBUG_UTIL)
     debug_return_size_t(strlcpy(str, user_shost, strsize));
 }
 
 static size_t
-fill_command(char *str, size_t strsize)
+fill_command(char *str, size_t strsize, char *unused)
 {
     debug_decl(fill_command, SUDO_DEBUG_UTIL)
     debug_return_size_t(strlcpy(str, user_base, strsize));
@@ -165,7 +166,9 @@ expand_iolog_path(const char *prefix, const char *dir, const char *file,
 {
     size_t len, prelen = 0;
     char *dst, *dst0, *path, *pathend, tmpbuf[PATH_MAX];
+    char *slash = NULL;
     const char *endbrace, *src = dir;
+    static struct path_escape *escapes;
     int pass;
     bool strfit;
     debug_decl(expand_iolog_path, SUDO_DEBUG_UTIL)
@@ -193,17 +196,20 @@ expand_iolog_path(const char *prefix, const char *dir, const char *file,
 	switch (pass) {
 	case 0:
 	    src = dir;
+	    escapes = io_path_escapes + 1; /* skip "${seq}" */
 	    break;
 	case 1:
 	    /* Trim trailing slashes from dir component. */
 	    while (dst - path - 1 > prelen && dst[-1] == '/')
 		dst--;
-	    if (slashp)
-		*slashp = dst;
-	    src = "/";
-	    break;
+	    /* The NUL will be replaced with a '/' at the end. */
+	    if (dst + 1 >= pathend)
+		goto bad;
+	    slash = dst++;
+	    continue;
 	case 2:
 	    src = file;
+	    escapes = io_path_escapes;
 	    break;
 	}
 	dst0 = dst;
@@ -220,7 +226,8 @@ expand_iolog_path(const char *prefix, const char *dir, const char *file,
 				break;
 			}
 			if (esc->name != NULL) {
-			    len = esc->copy_fn(dst, (size_t)(pathend - dst));
+			    len = esc->copy_fn(dst, (size_t)(pathend - dst),
+				path + prelen);
 			    if (len >= (size_t)(pathend - dst))
 				goto bad;
 			    dst += len;
@@ -275,6 +282,9 @@ expand_iolog_path(const char *prefix, const char *dir, const char *file,
 	    *dst = '\0';
 	}
     }
+    if (slashp)
+	*slashp = slash;
+    *slash = '/';
 
     debug_return_str(path);
 bad:
diff --git a/plugins/sudoers/regress/iolog_path/check_iolog_path.c b/plugins/sudoers/regress/iolog_path/check_iolog_path.c
index f8079adb1..374b5fb90 100644
--- a/plugins/sudoers/regress/iolog_path/check_iolog_path.c
+++ b/plugins/sudoers/regress/iolog_path/check_iolog_path.c
@@ -200,7 +200,7 @@ main(int argc, char *argv[])
     exit(errors);
 }
 
-void io_nextid(char *iolog_dir, char id[7])
+void io_nextid(char *iolog_dir, char *fallback, char id[7])
 {
     memcpy(id, sessid, sizeof(sessid));
 }
diff --git a/plugins/sudoers/sudoers.h b/plugins/sudoers/sudoers.h
index 420742d0b..b0152b851 100644
--- a/plugins/sudoers/sudoers.h
+++ b/plugins/sudoers/sudoers.h
@@ -296,7 +296,7 @@ int atobool(const char *str);
 int get_boottime(struct timeval *);
 
 /* iolog.c */
-void io_nextid(char *iolog_dir, char sessid[7]);
+void io_nextid(char *iolog_dir, char *iolog_dir_fallback, char sessid[7]);
 
 /* iolog_path.c */
 char *expand_iolog_path(const char *prefix, const char *dir, const char *file,