diff --git a/src/util/simple_mtx.h b/src/util/simple_mtx.h
index 1508bacb604..3cfb9ed05c2 100644
--- a/src/util/simple_mtx.h
+++ b/src/util/simple_mtx.h
@@ -137,7 +137,7 @@ simple_mtx_unlock(simple_mtx_t *mtx)
 }
 
 static inline void
-simple_mtx_assert_locked(simple_mtx_t *mtx)
+simple_mtx_assert_locked(ASSERTED simple_mtx_t *mtx)
 {
    assert(mtx->val);
 }