diff --git a/src/video/null_v.cpp b/src/video/null_v.cpp
index 787bb64feb..0ca0057762 100644
--- a/src/video/null_v.cpp
+++ b/src/video/null_v.cpp
@@ -51,7 +51,10 @@ void VideoDriver_Null::MainLoop()
 	uint i;
 
 	for (i = 0; i < this->ticks && ! _exit_game; i++) {
-		::GameLoop();
+		{
+			std::lock_guard<std::mutex> lock(this->game_state_mutex);
+			::GameLoop();
+		}
 		::InputLoop();
 		::UpdateWindows();
 	}