diff --git a/test/Test.hs b/test/Test.hs
index aafd26b..6492943 100644
--- a/test/Test.hs
+++ b/test/Test.hs
@@ -164,8 +164,11 @@ prop_ppDiffR (DiffInput le ri) =
     let haskDiff=ppDiff $ getGroupedDiff le ri
         utilDiff= unsafePerformIO (runDiff (unlines le) (unlines ri))
     in  cover 90 (haskDiff == utilDiff) "exact match" $
-                classify (haskDiff == utilDiff) "exact match"
-                        (div ((length (lines haskDiff))*100) (length (lines utilDiff)) < 110) -- less than 10% bigger
+                classify (haskDiff == utilDiff) "exact match" $
+                    div
+                      (length (lines haskDiff)*100)
+                      (max 1 $ length $ lines utilDiff)
+                    < 110 -- less than 10% bigger
     where
       runDiff left right =
           do leftFile <- writeTemp left