diff --git a/libc/string/memmove.c b/libc/string/memmove.c
index fb1d975..a9fc1b5 100644
--- a/libc/string/memmove.c
+++ b/libc/string/memmove.c
@@ -25,6 +25,7 @@
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
+#undef _FORTIFY_SOURCE
 #include <string.h>
 #include <strings.h>