diff --git a/find_path.c b/find_path.c
index 80836e5b3..bde5578e2 100644
--- a/find_path.c
+++ b/find_path.c
@@ -56,15 +56,15 @@ static char rcsid[] = "$Id$";
 #include "sudo.h"
 
 #ifndef STDC_HEADERS
-extern char *malloc();
-extern char *getenv();
-extern char *strcpy();
-extern int fprintf();
-extern int readlink();
-extern int stat();
-extern int lstat();
+extern char *malloc	__P((unsigned));
+extern char *getenv	__P((char *));
+extern char *strcpy	__P((char *, char *));
+extern int fprintf	__P((FILE *, const char *, ...));
+extern int readlink	__P((char *, char *, int));
+extern int stat		__P((char *, struct stat *));
+extern int lstat	__P((char *, struct stat *));
 #ifdef HAVE_STRDUP
-extern char *strdup();
+extern char *strdup	__P((char *));
 #endif /* HAVE_STRDUP */
 #endif /* !STDC_HEADERS */
 
diff --git a/getcwd.c b/getcwd.c
index 3b36c82cf..50eb311a2 100644
--- a/getcwd.c
+++ b/getcwd.c
@@ -55,9 +55,13 @@ static char rcsid[] = "$Id$";
 #include <sys/param.h>
 
 #ifndef STDC_HEADERS
-extern char *strcpy();
-extern int readlink();
-extern int lstat();
+extern char *strcpy	__P((char *, char *));
+extern int   strlen	__P((char *));
+extern char *getwd	__P((char *));
+extern char *malloc	__P((unsigned));
+extern FILE *popen	__P((char *, char *);
+extern int   pclose	__P((FILE *));
+extern char *fgets	__P((char *, int, FILE *));
 #endif /* !STDC_HEADERS */
 
 
diff --git a/getwd.c b/getwd.c
index 3b36c82cf..50eb311a2 100644
--- a/getwd.c
+++ b/getwd.c
@@ -55,9 +55,13 @@ static char rcsid[] = "$Id$";
 #include <sys/param.h>
 
 #ifndef STDC_HEADERS
-extern char *strcpy();
-extern int readlink();
-extern int lstat();
+extern char *strcpy	__P((char *, char *));
+extern int   strlen	__P((char *));
+extern char *getwd	__P((char *));
+extern char *malloc	__P((unsigned));
+extern FILE *popen	__P((char *, char *);
+extern int   pclose	__P((FILE *));
+extern char *fgets	__P((char *, int, FILE *));
 #endif /* !STDC_HEADERS */
 
 
diff --git a/strdup.c b/strdup.c
index b7376bec0..395f064c1 100644
--- a/strdup.c
+++ b/strdup.c
@@ -53,8 +53,8 @@ static char rcsid[] = "$Id$";
 #endif /* HAVE_MALLOC_H */
 
 #ifndef STDC_HEADERS
-extern char *malloc();
-extern char *strcpy();
+extern char *malloc	__P((unsigned));
+extern char *strcpy	__P((char *, char *));
 #endif /* !STDC_HEADERS */
 
 
diff --git a/sudo.c b/sudo.c
index 06b9eeaa9..5bfc749a0 100644
--- a/sudo.c
+++ b/sudo.c
@@ -85,9 +85,9 @@ static char rcsid[] = "$Id$";
 #include "version.h"
 
 #ifndef STDC_HEADERS
-extern char *malloc();
+extern char *malloc	__P((unsigned));
 #ifdef HAVE_STRDUP
-extern char *strdup();
+extern char *strdup	__P((char *));
 #endif /* HAVE_STRDUP */
 #endif /* STDC_HEADERS */
 
@@ -129,6 +129,7 @@ main(argc, argv)
 {
     int rtn;
     int sudo_mode = MODE_RUN;
+    extern char ** environ;
 
     Argv = argv;
     Argc = argc;