diff --git a/source/core/nodebuilder/nodebuild_utility.cpp b/source/core/nodebuilder/nodebuild_utility.cpp
index afc321668..9f6f7e674 100644
--- a/source/core/nodebuilder/nodebuild_utility.cpp
+++ b/source/core/nodebuilder/nodebuild_utility.cpp
@@ -115,11 +115,6 @@ void FNodeBuilder::MakeSegsFromSides ()
 {
 	int i, j;
 
-	if (Level.NumLines == 0)
-	{
-		I_Error ("Map is empty.\n");
-	}
-
 	for (i = 0; i < Level.NumLines; ++i)
 	{
 		if (Level.Lines[i].sidedef[0] != NULL)
diff --git a/source/core/sectorgeometry.cpp b/source/core/sectorgeometry.cpp
index 29d27991a..62af2902a 100644
--- a/source/core/sectorgeometry.cpp
+++ b/source/core/sectorgeometry.cpp
@@ -456,6 +456,14 @@ bool SectorGeometry::MakeVertices2(unsigned int secnum, int plane, const FVector
 nexti:;
 	}
 
+	if (lines.Size() == 0)
+	{
+		// nothing to generate.
+		auto& entry = data[secnum].planes[plane];
+		entry.vertices.Clear();
+		entry.texcoords.Clear();
+		return true;
+	}
 
 
 	FNodeBuilder::FLevel leveldata =