diff --git a/src/genworld.cpp b/src/genworld.cpp
--- a/src/genworld.cpp
+++ b/src/genworld.cpp
@@ -90,7 +90,6 @@ static void CleanupGeneration()
 
 	DeleteWindowById(WC_GENERATE_PROGRESS_WINDOW, 0);
 	MarkWholeScreenDirty();
-	_genworld_mapgen_mutex->EndCritical();
 }
 
 /**
@@ -179,6 +178,7 @@ static void _GenerateWorld(void *)
 		IncreaseGeneratingWorldProgress(GWP_GAME_START);
 
 		CleanupGeneration();
+		_genworld_mapgen_mutex->EndCritical();
 
 		ShowNewGRFError();