diff --git a/stl/src/mutex.cpp b/stl/src/mutex.cpp
index cd44a0044a7..4a35e8c77aa 100644
--- a/stl/src/mutex.cpp
+++ b/stl/src/mutex.cpp
@@ -147,8 +147,9 @@ static _Thrd_result mtx_do_lock(_Mtx_t mtx, const _timespec64* target) noexcept
 }
 
 _CRTIMP2_PURE _Thrd_result __cdecl _Mtx_unlock(_Mtx_t mtx) noexcept { // unlock mutex
+    _THREAD_ASSERT(mtx->_Count > 0, "unlock of unowned mutex");
     _THREAD_ASSERT(
-        1 <= mtx->_Count && mtx->_Thread_id == static_cast<long>(GetCurrentThreadId()), "unlock of unowned mutex");
+        mtx->_Thread_id == static_cast<long>(GetCurrentThreadId()), "unlock of mutex not owned by the current thread");
 
     if (--mtx->_Count == 0) { // leave critical section
         mtx->_Thread_id = -1;