--- a/configure.ac
+++ b/configure.ac
@@ -43,7 +43,8 @@ CC="$withval")
 
 AC_MSG_CHECKING([for additional required compiler flags])
 AC_TRY_RUN([#include <stdio.h>
-  main() {
+  #include <stdlib.h>
+  int main() {
   #ifdef __SUNPRO_C
         exit(0);
   #else
@@ -105,7 +106,8 @@ dirseparator="$withval", dirseparator="")
 AC_MSG_CHECKING([for path separator character])
 if test "$pathseparator" = "" ; then
   AC_TRY_RUN([#include <stdio.h>
-    main() {
+    #include <stdlib.h>
+    int main() {
     #ifdef _WIN32
 	  exit(0);
     #else
@@ -119,7 +121,8 @@ echo $pathseparator
 AC_MSG_CHECKING([for dir separator character])
 if test "$dirseparator" = "" ; then
   AC_TRY_RUN([#include <stdio.h>
-    main() {
+    #include <stdlib.h>
+    int main() {
     #ifdef _WIN32
 	  exit(0);
     #else
@@ -145,7 +148,8 @@ AC_MSG_CHECKING([for 64 bit types])
 # if used with the (correct) value -9223372036854775808LL.
 #
 AC_TRY_RUN([#include <stdio.h>
-      main() {
+      #include <stdlib.h>
+      int main() {
 	  long long ll;
 	  unsigned long long ull;
 	  exit(0);