1 files changed, 1 insertions, 0 deletions
diff --git a/AD.hs b/AD.hs
index 76fefe4..c9ac72e 100644
--- a/AD.hs
+++ b/AD.hs
@@ -99,6 +99,7 @@ ad' env = \case
       | TArray sht _ <- typeof e
       , Refl <- prfDualSht sht
       -> Shape (ad' env e)
+    Undef t -> Undef (dual t)
 
 convIdx :: DEnv env env' -> Idx env a -> Either (Idx env' a) (Idx env' (Dual a))
 convIdx ETop i = Left i