diff --git a/semantic-python/src/Language/Python/Core.hs b/semantic-python/src/Language/Python/Core.hs
index 11ea4afe0..852eae912 100644
--- a/semantic-python/src/Language/Python/Core.hs
+++ b/semantic-python/src/Language/Python/Core.hs
@@ -27,13 +27,13 @@ instance (Compile l, Compile r) => Compile (Either l r) where compile = compileS
 instance Compile Py.AssertStatement
 instance Compile Py.Attribute
 
--- TODO what is this third field here
 instance Compile Py.Assignment where
   compile (Py.Assignment (Py.ExpressionList [lhs]) (Just rhs) _) = do
     target <- compile lhs
     value  <- compile rhs
     pure (target .= value)
   compile (Py.Assignment (Py.ExpressionList hs) _ _) = fail ("too many lhs values: " <> show (length hs))
+  compile other = fail ("Unhandled assignment case: " <> show other)
 
 instance Compile Py.AugmentedAssignment
 instance Compile Py.Await