diff --git a/src/g_levellocals.h b/src/g_levellocals.h
index 1574442d6c..f83d6d6f81 100644
--- a/src/g_levellocals.h
+++ b/src/g_levellocals.h
@@ -118,7 +118,7 @@ struct FLevelLocals
 
 	node_t		*HeadNode() const
 	{
-		return &nodes[nodes.Size() - 1];
+		return nodes.Size() == 0? nullptr : &nodes[nodes.Size() - 1];
 	}
 	node_t		*HeadGamenode() const
 	{
diff --git a/src/p_setup.cpp b/src/p_setup.cpp
index d420ce2af2..eccad199e0 100644
--- a/src/p_setup.cpp
+++ b/src/p_setup.cpp
@@ -3957,7 +3957,7 @@ void P_SetupLevel (const char *lumpname, int position)
 	}
 
 	// set the head node for gameplay purposes. If the separate gamenodes array is not empty, use that, otherwise use the render nodes.
-	level.headgamenode = level.gamenodes.Size() > 0 ? &level.gamenodes[level.gamenodes.Size() - 1] : &level.nodes[level.nodes.Size() - 1];
+	level.headgamenode = level.gamenodes.Size() > 0 ? &level.gamenodes[level.gamenodes.Size() - 1] : level.nodes.Size()? &level.nodes[level.nodes.Size() - 1] : nullptr;
 
 	times[10].Clock();
 	P_LoadBlockMap (map);