diff --git a/+misc/subsurf.m b/+misc/subsurf.m
index cb6a46d96b8652395f30df86f0ae9f9d41e4254f..41387825e50ea83ccaa13743bfa8fdaa9862281b 100644
--- a/+misc/subsurf.m
+++ b/+misc/subsurf.m
@@ -50,7 +50,8 @@ end
 doCompare = ~isempty(myParser.Results.compareWith);
 if doCompare
 	dataReference = permute(myParser.Results.compareWith, [restDim, xDim, yDim]);
-	assert(isequal(size(dataReference), size(data)));
+	assert(isequal(size(dataReference), size(data)), ...
+		"size(data)="+num2str(size(data))+"~=size(compareWith)="+num2str(size(dataReference)));
 end
 
 %% plot