diff --git a/src/system.h.in b/src/system.h.in
index 0675912..a946d3a 100644
--- a/src/system.h.in
+++ b/src/system.h.in
@@ -22,10 +22,6 @@
 
 #define _FILE_OFFSET_BITS 64
 
-#ifndef _GNU_SOURCE
-#define _GNU_SOURCE
-#endif
-
 #if defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__) || defined(__bsdi__) || defined(__DragonFly__) || (defined(__APPLE__) && defined(__MACH__)) || defined(__FreeBSD_kernel__)
 #define BSD_LIKE
 #endif