diff --git a/libxml.m4 b/libxml.m4
index ed13cff..afffd39 100644
--- a/libxml.m4
+++ b/libxml.m4
@@ -59,6 +59,7 @@
       AC_TRY_RUN([
 #include <stdlib.h>
 #include <stdio.h>
+#include <string.h>
 #include <libxml/tree.h>
 
 int 
@@ -253,6 +254,7 @@
       AC_TRY_RUN([
 #include <stdlib.h>
 #include <stdio.h>
+#include <string.h>
 #include <libxml/xmlversion.h>
 
 int