diff --git a/src/p_terrain.cpp b/src/p_terrain.cpp
index af8de5cab..d30354c1e 100644
--- a/src/p_terrain.cpp
+++ b/src/p_terrain.cpp
@@ -627,13 +627,19 @@ static void ParseFloor (FScanner &sc)
 	FTextureID picnum;
 	int terrain;
 
+	bool opt = sc.CheckString("optional");
 	sc.MustGetString ();
+
 	picnum = TexMan.CheckForTexture (sc.String, FTexture::TEX_Flat,
 		FTextureManager::TEXMAN_Overridable|FTextureManager::TEXMAN_TryAny);
+
 	if (!picnum.Exists())
 	{
-		Printf ("Unknown flat %s\n", sc.String);
-		sc.MustGetString ();
+		sc.MustGetString();
+		if (!opt)
+		{
+			Printf("Unknown flat %s\n", sc.String);
+		}
 		return;
 	}
 	sc.MustGetString ();