--- a/diff/system.h
+++ b/diff/system.h
@@ -177,7 +177,7 @@
 VOID *realloc ();
 #endif
 #ifndef getenv
-char *getenv ();
+char *getenv (const char *);
 #endif
 
 #include <limits.h>
--- a/diff/util.c
+++ b/diff/util.c
@@ -24,7 +24,7 @@
 #endif
 
 #ifndef strerror
-extern char *strerror ();
+extern char *strerror (int);
 #endif
 
 /* Queue up one-line messages to be printed at the end,
--- a/lib/getopt.c
+++ b/lib/getopt.c
@@ -124,7 +124,7 @@
    whose names are inconsistent.  */
 
 #ifndef getenv
-extern char *getenv ();
+extern char *getenv (const char *);
 #endif
 
 #endif /* not __GNU_LIBRARY__ */
--- a/lib/sighandle.c
+++ b/lib/sighandle.c
@@ -56,7 +56,7 @@
 
 /* Define linked list of signal handlers structure */
 struct SIG_hlist {
-	RETSIGTYPE		(*handler)();
+	RETSIGTYPE		(*handler)(int);
 	struct SIG_hlist	*next;
 };
 
@@ -220,7 +220,7 @@
  * restoration later.
  */
 
-int SIG_register(int sig, RETSIGTYPE (*fn)())
+int SIG_register(int sig, RETSIGTYPE (*fn)(int))
 {
 	int			val;
 	struct SIG_hlist	*this;