diff --git a/Source/Plugins/BuilderModes/VisualModes/EffectSRB2ThingVertexSlope.cs b/Source/Plugins/BuilderModes/VisualModes/EffectSRB2ThingVertexSlope.cs
index ddd33e2..3d0a47a 100644
--- a/Source/Plugins/BuilderModes/VisualModes/EffectSRB2ThingVertexSlope.cs
+++ b/Source/Plugins/BuilderModes/VisualModes/EffectSRB2ThingVertexSlope.cs
@@ -57,7 +57,7 @@ namespace CodeImp.DoomBuilder.BuilderModes
 				if (t.Parameter > 0)
 					position.z = t.GetFlagsValue();
 				else
-					position.z = (t.Sector != null) ? t.Sector.FloorHeight : 0;
+					position.z += (t.Sector != null) ? t.Sector.FloorHeight : 0;
                 verts[index] = position;
                 index++;
                 if (index > 2) break; //Only the first three vertices are used