diff --git a/lib/strequal.c b/lib/strequal.c
index adf84403d..49dc4880b 100644
--- a/lib/strequal.c
+++ b/lib/strequal.c
@@ -21,6 +21,11 @@
  * $Id$
  ***************************************************************************/
 
+#ifndef _GNU_SOURCE
+/* glibc needs this to define the prototype for strcasestr */
+#define _GNU_SOURCE 1
+#endif
+
 #include "setup.h"
 
 #include <string.h>