diff --git a/mbtiles.cpp b/mbtiles.cpp
index 697630c9..80153340 100644
--- a/mbtiles.cpp
+++ b/mbtiles.cpp
@@ -1,5 +1,7 @@
 // for vasprintf() on Linux
+#ifndef _GNU_SOURCE
 #define _GNU_SOURCE
+#endif
 
 #include <stdio.h>
 #include <stdlib.h>