diff --git a/lib/Properties.hs b/lib/Properties.hs
index 1d01216795ad5e84fafdabe4fb486e23c94f2828..0bd3d55c02a22bcb905d0752942e08b25199097f 100644
--- a/lib/Properties.hs
+++ b/lib/Properties.hs
@@ -73,7 +73,7 @@ checkMap = do
     $ complain "The map's tile size must be 32 by 32 pixels."
 
   unlessHasProperty "mapCopyright"
-    $ complain "must give the map's copyright via the \"mapCopyright\" property."
+    $ suggest "document the map's copyright via the \"mapCopyright\" property."
 
   -- TODO: this doesn't catch collisions with the default start layer!
   whenLayerCollisions (\(Property name _) -> name == "exitUrl" || name == "startLayer")