--- a/src/string.c	Wed Dec 17 20:13:08 2025 +0100
+++ b/src/string.c	Thu Dec 18 12:11:30 2025 +0100
@@ -26,8 +26,9 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-// for memrchr in glibc
+#ifdef WITH_MEMRCHR
 #define _GNU_SOURCE
+#endif
 
 #include "cx/string.h"