diff --git a/UNITTESTS/stubs/Mutex_stub.cpp b/UNITTESTS/stubs/Mutex_stub.cpp
index c287d3bec03..cd226064f8e 100644
--- a/UNITTESTS/stubs/Mutex_stub.cpp
+++ b/UNITTESTS/stubs/Mutex_stub.cpp
@@ -27,7 +27,12 @@ rtos::Mutex::~Mutex()
     return;
 }
 
-osStatus rtos::Mutex::lock(unsigned int)
+osStatus rtos::Mutex::lock(void)
+{
+    return osOK;
+}
+
+osStatus rtos::Mutex::lock(uint32_t millisec)
 {
     return osOK;
 }