diff --git a/compiler/Type/Constrain/Expression.hs b/compiler/Type/Constrain/Expression.hs
index 21389e5..aa5df70 100644
--- a/compiler/Type/Constrain/Expression.hs
+++ b/compiler/Type/Constrain/Expression.hs
@@ -36,10 +36,10 @@ constrain env (A region expr) tipe =
           | otherwise           -> return (name <? tipe)
 
       Range lo hi ->
-          exists $ \x -> do
-            clo <- constrain env lo x
-            chi <- constrain env hi x
-            return $ and [clo, chi, list x === tipe]
+          existsNumber $ \n -> do
+            clo <- constrain env lo n
+            chi <- constrain env hi n
+            return $ and [clo, chi, list n === tipe]
 
       ExplicitList exprs ->
           exists $ \x -> do
diff --git a/compiler/Type/Type.hs b/compiler/Type/Type.hs
index 023ecd3..55ec193 100644
--- a/compiler/Type/Type.hs
+++ b/compiler/Type/Type.hs
@@ -141,6 +141,11 @@ exists f = do
   v <- liftIO $ var Flexible
   ex [v] <$> f (VarN v)
 
+existsNumber :: Error e => (Type -> ErrorT e IO TypeConstraint) -> ErrorT e IO TypeConstraint
+existsNumber f = do
+  v <- liftIO $ var (Is Number)
+  ex [v] <$> f (VarN v)
+
 
 instance Show a => Show (UF.Point a) where
   show point = unsafePerformIO $ fmap show (UF.descriptor point)