diff --git a/test/InterpreterSpec.hs b/test/InterpreterSpec.hs
index 81ec79485..2cb4f0a34 100644
--- a/test/InterpreterSpec.hs
+++ b/test/InterpreterSpec.hs
@@ -13,6 +13,7 @@ import Syntax
 import Term.Arbitrary
 import Test.Hspec
 import Test.Hspec.QuickCheck
+import Test.QuickCheck
 
 spec :: Spec
 spec = parallel $ do
@@ -39,10 +40,10 @@ spec = parallel $ do
           Pure a -> pure a
     let toTerm' c (ArbitraryTerm r f) = decorate (toTerm (ArbitraryTerm (setCategory r c) f))
     let root = cofree . ((pure 0 .: Program .: RNil) :<) . Indexed
-    prop "produces unbiased deletions" $
-      \ a b c -> let (a', b') = (toTerm' c a, toTerm' c (b :: ArbitraryTerm Text (Record '[Category]))) in
+    prop "produces unbiased deletions" . forAll (arbitrary `suchThat` \ (a, b, _) -> syntax a /= syntax b) $
+      \ (a, b, c) -> let (a', b') = (toTerm' c a, toTerm' c (b :: ArbitraryTerm Text (Record '[Category]))) in
         stripDiff (diffTerms wrap compare diffCost (root [ a', b' ]) (root [ a' ])) `shouldBe` reverse' (stripDiff (diffTerms wrap compare diffCost (root [ b', a' ]) (root [ a' ])))
 
-    prop "produces unbiased insertions" $
-      \ a b c -> let (a', b') = (toTerm' c a, toTerm' c (b :: ArbitraryTerm Text (Record '[Category]))) in
+    prop "produces unbiased insertions" . forAll (arbitrary `suchThat` \ (a, b, _) -> syntax a /= syntax b) $
+      \ (a, b, c) -> let (a', b') = (toTerm' c a, toTerm' c (b :: ArbitraryTerm Text (Record '[Category]))) in
         stripDiff (diffTerms wrap compare diffCost (root [ a' ]) (root [ a', b' ])) `shouldBe` reverse' (stripDiff (diffTerms wrap compare diffCost (root [ a' ]) (root [ b', a' ])))