diff --git a/rt/tst-timer4.c b/rt/tst-timer4.c
index 78c8744726..2175211cb6 100644
--- a/rt/tst-timer4.c
+++ b/rt/tst-timer4.c
@@ -21,6 +21,7 @@
 #include <errno.h>
 #include <signal.h>
 #include <stdio.h>
+#include <string.h>
 #include <time.h>
 #include <unistd.h>
 #if _POSIX_THREADS