diff --git a/graph.cpp b/graph.cpp
index da33fcea..bda270f5 100644
--- a/graph.cpp
+++ b/graph.cpp
@@ -3946,7 +3946,6 @@ EX int ceiling_category(cell *c) {
     case laEFire:
     case laEEarth:
     case laElementalWall:
-    case laCanvas:
     case laTrollheim:
     case laDungeon:
     case laBull:
@@ -3958,6 +3957,10 @@ EX int ceiling_category(cell *c) {
     case laSwitch:
     case laEclectic:
       return 3;
+
+    case laCanvas:
+      if(canvas_default_wall == waInvisibleFloor) return 0;
+      return 3;
     
     case laPalace:
     case laPrincessQuest: