diff --git a/Foundation/include/Poco/Thread_WIN32.h b/Foundation/include/Poco/Thread_WIN32.h
index ec9e43746..cc328c778 100644
--- a/Foundation/include/Poco/Thread_WIN32.h
+++ b/Foundation/include/Poco/Thread_WIN32.h
@@ -42,6 +42,7 @@
 
 #include "Poco/Foundation.h"
 #include "Poco/Runnable.h"
+#include "Poco/Mutex.h"
 #include "Poco/UnWindows.h"
 
 
@@ -117,6 +118,7 @@ private:
 	HANDLE       _thread;
 	int          _prio;
 	std::size_t  _stackSize;
+	Mutex        _mutex;
 
 	static DWORD _currentKey;
 };
diff --git a/Foundation/src/Thread_WIN32.cpp b/Foundation/src/Thread_WIN32.cpp
index 39452bc6c..f29d9eba2 100644
--- a/Foundation/src/Thread_WIN32.cpp
+++ b/Foundation/src/Thread_WIN32.cpp
@@ -83,6 +83,8 @@ void ThreadImpl::setPriorityImpl(int prio)
 
 void ThreadImpl::startImpl(Runnable& target)
 {
+	Mutex::ScopedLock lock(_mutex);
+
 	if (isRunningImpl())
 		throw SystemException("thread already running");
 
@@ -94,6 +96,8 @@ void ThreadImpl::startImpl(Runnable& target)
 
 void ThreadImpl::startImpl(Callback target, void* pData)
 {
+	Mutex::ScopedLock lock(_mutex);
+
 	if (isRunningImpl())
 		throw SystemException("thread already running");