diff --git a/sys/tests/ktest.c b/sys/tests/ktest.c
index fcb40130bcef..495fedf95dde 100644
--- a/sys/tests/ktest.c
+++ b/sys/tests/ktest.c
@@ -32,6 +32,7 @@
 #include <sys/types.h>
 #include <sys/kernel.h>
 #include <sys/lock.h>
+#include <sys/mutex.h>
 #include <sys/malloc.h>
 #include <sys/module.h>
 #include <sys/socket.h>