diff --git a/src/DiffSummary.hs b/src/DiffSummary.hs
index 9bce68607..0c40a26fd 100644
--- a/src/DiffSummary.hs
+++ b/src/DiffSummary.hs
@@ -108,7 +108,7 @@ instance HasCategory Category where
 instance (HasCategory leaf, HasField fields Category) => HasCategory (Term leaf (Record fields)) where
   toCategoryName = toCategoryName . category . extract
 
-data Branch = BIndexed | BFixed | BCommented deriving (Show, Eq, Generic)
+data Branch = BIndexed | BFixed | BCommented | BError deriving (Show, Eq, Generic)
 instance Arbitrary Branch where
   arbitrary = oneof [ pure BIndexed, pure BFixed ]
   shrink = genericShrink