diff --git a/mstorage_add.c b/mstorage_add.c
index 80d40f6..fbe3195 100644
--- a/mstorage_add.c
+++ b/mstorage_add.c
@@ -1,4 +1,6 @@
+#ifndef _GNU_SOURCE
 #define _GNU_SOURCE
+#endif
 #include <stdlib.h>
 #include <unistd.h>
 #include <sys/mman.h>
diff --git a/tinyldap.c b/tinyldap.c
index 32d2e16..c7446a5 100644
--- a/tinyldap.c
+++ b/tinyldap.c
@@ -1,4 +1,6 @@
+#ifndef _GNU_SOURCE
 #define _GNU_SOURCE
+#endif
 #define _FILE_OFFSET_BITS 64
 #include <unistd.h>
 #include <stdlib.h>