diff --git a/wadsrc/static/zscript/level_postprocessor.zs b/wadsrc/static/zscript/level_postprocessor.zs
index 9b3b7b7507..93ee8343de 100644
--- a/wadsrc/static/zscript/level_postprocessor.zs
+++ b/wadsrc/static/zscript/level_postprocessor.zs
@@ -52,13 +52,19 @@ class LevelPostProcessor native play
 	protected native void SetLineSectorRef(uint line, uint side, uint sector);
 	protected native Actor GetDefaultActor(Name actorclass);
 
-	protected void FlipLine(uint Line)
+	protected void FlipLineVertexes(uint Line)
 	{
 		uint v1 = level.lines[Line].v1.Index();
 		uint v2 = level.lines[Line].v2.Index();
 		SetLineVertexes(Line, v2, v1);
 	}
 
+	protected void FlipLineCompletely(uint Line)
+	{
+		FlipLineVertexes(Line);
+		FlipLineSideRefs(Line);
+	}
+
 	protected void SetWallTexture(int line, int side, int texpart, String texture)
 	{
 		SetWallTextureID(line, side, texpart, TexMan.CheckForTexture(texture, TexMan.Type_Wall));