--- a/acinclude.m4
+++ b/acinclude.m4
@@ -953,6 +953,7 @@ changequote(<<, >>)dnl
 #include <stdio.h>
 #include <sys/types.h>
 #include <signal.h>
+#include <stdlib>
 
 int main(int argc, char *argv[])
 {
@@ -1001,6 +1002,7 @@ changequote(<<, >>)dnl
 #include <stdio.h>
 #include <sys/types.h>
 #include <unistd.h>
+#include <stdlib.h>
 int main(int argc, char *argv[])
 {
     FILE *fp;