diff --git a/libctf/testsuite/libctf-regression/open-error-free.c b/libctf/testsuite/libctf-regression/open-error-free.c
index 7405cdb25f3..0cf55ad157b 100644
--- a/libctf/testsuite/libctf-regression/open-error-free.c
+++ b/libctf/testsuite/libctf-regression/open-error-free.c
@@ -1,6 +1,5 @@
 /* Make sure that, on error, an opened dict is properly freed.  */
 
-#define _GNU_SOURCE 1
 #include "config.h"
 #include <dlfcn.h>
 #include <stdio.h>