diff --git a/semantic-ast/src/AST/Unmarshal.hs b/semantic-ast/src/AST/Unmarshal.hs
index 190086c51..169aed615 100644
--- a/semantic-ast/src/AST/Unmarshal.hs
+++ b/semantic-ast/src/AST/Unmarshal.hs
@@ -220,11 +220,6 @@ class UnmarshalField t where
     -> [Node] -- ^ nodes
     -> MatchM (t (f ann))
 
-instance UnmarshalField Err where
-  unmarshalField _ _ [] = pure $ Fail "No items provided to unmarshalField."
-  unmarshalField _ _ [x] = Succeed <$> unmarshalNode x
-  unmarshalField d f _ = pure $ Fail ("type '" <> d <> "' expected zero or one nodes in field '" <> f <> "' but got multiple")
-
 instance UnmarshalField Maybe where
   unmarshalField _ _ []  = pure Nothing
   unmarshalField _ _ [x] = Just <$> unmarshalNode x