2 files changed, 8 insertions, 4 deletions
diff --git a/common/util.cpp b/common/util.cpp
index 548fcb6a41..8920453bd7 100644
--- a/common/util.cpp
+++ b/common/util.cpp
@@ -166,7 +166,10 @@ uint RandomSource::getRandomNumberRng(uint min, uint max) {
 	return getRandomNumber(max - min) + min;
 }
 
-StackLock::StackLock(OSystem::MutexRef mutex) : _mutex(mutex) {
+StackLock::StackLock(OSystem::MutexRef mutex, OSystem *syst)
+	: _mutex(mutex), _syst(syst) {
+	if (syst == 0)
+		_syst = g_system;
 	lock();
 }
 
@@ -175,12 +178,12 @@ StackLock::~StackLock() {
 }
 
 void StackLock::lock() {
-	assert(g_system);
+	assert(_syst);
 	g_system->lock_mutex(_mutex);
 }
 
 void StackLock::unlock() {
-	assert(g_system);
+	assert(_syst);
 	g_system->unlock_mutex(_mutex);
 }
 
diff --git a/common/util.h b/common/util.h
index 8c0409e0ef..3a77445567 100644
--- a/common/util.h
+++ b/common/util.h
@@ -80,10 +80,11 @@ public:
  */
 class StackLock {
 	OSystem::MutexRef _mutex;
+	OSystem *_syst;
 	void lock();
 	void unlock();
 public:
-	StackLock(OSystem::MutexRef mutex);
+	StackLock(OSystem::MutexRef mutex, OSystem *syst = 0);
 	~StackLock();
 };