diff --git a/libiberty/acinclude.m4 b/libiberty/acinclude.m4
index 6bd127e98268..6bb690597bfb 100644
--- a/libiberty/acinclude.m4
+++ b/libiberty/acinclude.m4
@@ -24,6 +24,8 @@ AC_CACHE_CHECK([for working strncmp], ac_cv_func_strncmp_works,
 [AC_TRY_RUN([
 /* Test by Jim Wilson and Kaveh Ghazi.
    Check whether strncmp reads past the end of its string parameters. */
+#include <stdlib.h>
+#include <string.h>
 #include <sys/types.h>
 
 #ifdef HAVE_FCNTL_H
@@ -51,7 +53,8 @@ AC_CACHE_CHECK([for working strncmp], ac_cv_func_strncmp_works,
 
 #define MAP_LEN 0x10000
 
-main ()
+int
+main (void)
 {
 #if defined(HAVE_MMAP) || defined(HAVE_MMAP_ANYWHERE)
   char *p;
@@ -157,7 +160,10 @@ if test $ac_cv_os_cray = yes; then
 fi
 
 AC_CACHE_CHECK(stack direction for C alloca, ac_cv_c_stack_direction,
-[AC_TRY_RUN([find_stack_direction ()
+[AC_TRY_RUN([#include <stdlib.h>
+
+int
+find_stack_direction (void)
 {
   static char *addr = 0;
   auto char dummy;
@@ -169,7 +175,9 @@ AC_CACHE_CHECK(stack direction for C alloca, ac_cv_c_stack_direction,
   else
     return (&dummy > addr) ? 1 : -1;
 }
-main ()
+
+int
+main (void)
 {
   exit (find_stack_direction() < 0);
 }],
diff --git a/libiberty/configure b/libiberty/configure
index 65fc50020027..860f981fa183 100755
--- a/libiberty/configure
+++ b/libiberty/configure
@@ -6784,7 +6784,10 @@ else
 else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-find_stack_direction ()
+#include <stdlib.h>
+
+int
+find_stack_direction (void)
 {
   static char *addr = 0;
   auto char dummy;
@@ -6796,7 +6799,9 @@ find_stack_direction ()
   else
     return (&dummy > addr) ? 1 : -1;
 }
-main ()
+
+int
+main (void)
 {
   exit (find_stack_direction() < 0);
 }
@@ -7621,6 +7626,8 @@ else
 
 /* Test by Jim Wilson and Kaveh Ghazi.
    Check whether strncmp reads past the end of its string parameters. */
+#include <stdlib.h>
+#include <string.h>
 #include <sys/types.h>
 
 #ifdef HAVE_FCNTL_H
@@ -7648,7 +7655,8 @@ else
 
 #define MAP_LEN 0x10000
 
-main ()
+int
+main (void)
 {
 #if defined(HAVE_MMAP) || defined(HAVE_MMAP_ANYWHERE)
   char *p;