diff --git a/source/tools/atlas/GameInterface/GameLoop.cpp b/source/tools/atlas/GameInterface/GameLoop.cpp
index 9104d5eb65..484a4d2853 100644
--- a/source/tools/atlas/GameInterface/GameLoop.cpp
+++ b/source/tools/atlas/GameInterface/GameLoop.cpp
@@ -144,9 +144,9 @@ static void* RunEngine(void* data)
 		{
 			double time = timer_Time();
 			static double last_time = time;
-			float realFrameLength = (float)(time-last_time);
+			// TODO: why is this sometimes negative, if timer_Time ensures monotonic results?
+			float realFrameLength = std::max(0.0f, (float)(time-last_time));
 			last_time = time;
-			ENSURE(realFrameLength >= 0.0f);
 			// TODO: filter out big jumps, e.g. when having done a lot of slow
 			// processing in the last frame
 			state.realFrameLength = realFrameLength;