diff --git a/src/Control/Monad/Supply.hs b/src/Control/Monad/Supply.hs
index 1aa36ae..8d46d92 100644
--- a/src/Control/Monad/Supply.hs
+++ b/src/Control/Monad/Supply.hs
@@ -47,9 +47,14 @@ newtype Supply s a = Supply (SupplyT s Identity a)
   deriving (Functor, Applicative, Monad, MonadSupply s, MonadFix)
 
 instance Monad m => MonadSupply s (SupplyT s m) where
-  supply = SupplyT $ do (x:xs) <- get
-                        put xs
-                        return x
+  supply =
+    SupplyT $ do
+      result <- get
+      case result of
+        (x:xs) -> do
+          put xs
+          return x
+        _ -> error "Exhausted supply in Control.Monad.Supply.hs"
   peek = SupplyT $ gets head
   exhausted = SupplyT $ gets null
 
diff --git a/src/Duet/Infer.hs b/src/Duet/Infer.hs
index f625e68..d9010fe 100644
--- a/src/Duet/Infer.hs
+++ b/src/Duet/Infer.hs
@@ -901,7 +901,7 @@ inferExpressionType ce as (ApplicationExpression l e f) = do
   let scheme = (Forall [] (Qualified (ps++qs) t))
   return (ps ++ qs, t, ApplicationExpression (TypeSignature l scheme) e' f')
 inferExpressionType ce as (InfixExpression l x (i,op) y) = do
-  (ps, ts, ApplicationExpression l' (ApplicationExpression _ (op') x') y') <-
+  (ps, ts, ~(ApplicationExpression l' (ApplicationExpression _ (op') x') y')) <-
     inferExpressionType
       ce
       as