diff --git a/src/eap-peap.c b/src/eap-peap.c
index 785bfc81..45590668 100644
--- a/src/eap-peap.c
+++ b/src/eap-peap.c
@@ -24,6 +24,7 @@
 #include <config.h>
 #endif
 
+#define _GNU_SOURCE
 #include <string.h>
 #include <stdio.h>
 #include <errno.h>