diff --git a/src/knownnetworks.c b/src/knownnetworks.c
index 6f65d2b3..886f8145 100644
--- a/src/knownnetworks.c
+++ b/src/knownnetworks.c
@@ -24,6 +24,7 @@
 #include <config.h>
 #endif
 
+#define _GNU_SOURCE
 #include <sys/types.h>
 #include <dirent.h>
 #include <errno.h>