diff --git a/compiler/Build/Source.hs b/compiler/Build/Source.hs
index 08656b6..56ec622 100644
--- a/compiler/Build/Source.hs
+++ b/compiler/Build/Source.hs
@@ -2,7 +2,6 @@
 module Build.Source (build) where
 
 import qualified Data.Map as Map
-import qualified Data.Set as Set
 import System.FilePath as FP
 import Text.PrettyPrint (Doc)
 
@@ -33,7 +32,7 @@ build noPrelude interfaces source =
 
      let exports'
              | null exs =
-                 let get = Set.toList . Pattern.boundVars in
+                 let get = Pattern.boundVarList in
                  concat [ get pattern | Definition (Expr.Definition pattern _ _) <- decls ] ++
                  concat [ map fst ctors | Datatype _ _ ctors <- decls ] ++
                  [ name | TypeAlias name _ (Type.Record _ _) <- decls ]
diff --git a/compiler/Transform/Check.hs b/compiler/Transform/Check.hs
index 490c7f7..057537f 100644
--- a/compiler/Transform/Check.hs
+++ b/compiler/Transform/Check.hs
@@ -32,7 +32,7 @@ dupErr err x =
 
 duplicates :: [D.Declaration] -> [String]
 duplicates decls =
-    map msg (dups (portNames ++ concatMap getNames defPatterns)) ++
+    map msg (dups (portNames ++ concatMap Pattern.boundVarList defPatterns)) ++
     case mapM exprDups (portExprs ++ defExprs) of
       Left name -> [msg name]
       Right _   -> []
@@ -50,14 +50,13 @@ duplicates decls =
               D.Out name expr _ -> (name, [expr])
               D.In name _ -> (name, [])
 
-    getNames = Set.toList . Pattern.boundVars
-
-    exprDups :: E.LExpr -> Either String E.LExpr
+    exprDups :: E.Expr -> Either String E.Expr
     exprDups expr = Expr.crawlLet defsDups expr
 
     defsDups :: [E.Def] -> Either String [E.Def]
     defsDups defs =
-        case dups $ concatMap (\(E.Definition name _ _) -> getNames name) defs of
+        let varsIn (E.Definition pattern _ _) = Pattern.boundVarList pattern in
+        case dups $ concatMap varsIn defs of
           []     -> Right defs
           name:_ -> Left name