diff --git a/src/debug.c b/src/debug.c
index 82638f83..6f0b5e70 100644
--- a/src/debug.c
+++ b/src/debug.c
@@ -40,7 +40,6 @@
 #include <fcntl.h>
 #include "bio.h"
 #include <unistd.h>
-#define _GNU_SOURCE
 #include <dlfcn.h>
 #endif /* HAVE_BACKTRACE */