--- a/libupnpp/md5.cxx
+++ b/libupnpp/md5.cxx
@@ -27,6 +27,8 @@
  * This code is the same as the code published by RSA Inc.  It has been
  * edited for clarity and style only.
  */
+#include "config.h"
+
 #include <stdio.h>
 #include <string.h>