diff --git a/src/Juvix/Compiler/Concrete/Data/NameSignature/Builder.hs b/src/Juvix/Compiler/Concrete/Data/NameSignature/Builder.hs
index 1960655531..ace4a4ec24 100644
--- a/src/Juvix/Compiler/Concrete/Data/NameSignature/Builder.hs
+++ b/src/Juvix/Compiler/Concrete/Data/NameSignature/Builder.hs
@@ -15,6 +15,7 @@ where
 
 import Juvix.Compiler.Concrete.Data.NameSignature.Error
 import Juvix.Compiler.Concrete.Gen qualified as Gen
+import Juvix.Compiler.Concrete.Language.Base
 import Juvix.Compiler.Concrete.Translation.FromParsed.Analysis.Scoping.Error
 import Juvix.Prelude
 
@@ -64,9 +65,7 @@ instance (SingI s) => HasNameSignature s (AxiomDef s) where
   addArgs a = addArgs (a ^. axiomTypeSig)
 
 instance (SingI s) => HasNameSignature s (FunctionLhs s) where
-  addArgs a = do
-    mapM_ addSigArg (a ^. funLhsArgs)
-    whenJust (a ^. funLhsRetType) addExpressionType
+  addArgs FunctionLhs {..} = addArgs _funLhsTypeSig
 
 instance (SingI s) => HasNameSignature s (FunctionDef s) where
   addArgs = addArgs . functionDefLhs
diff --git a/src/Juvix/Compiler/Concrete/Extra.hs b/src/Juvix/Compiler/Concrete/Extra.hs
index 2c049b1e7b..cf8dcdcbb4 100644
--- a/src/Juvix/Compiler/Concrete/Extra.hs
+++ b/src/Juvix/Compiler/Concrete/Extra.hs
@@ -111,7 +111,7 @@ isBodyExpression = \case
   SigBodyClauses {} -> False
 
 isLhsFunctionLike :: FunctionLhs 'Parsed -> Bool
-isLhsFunctionLike FunctionLhs {..} = notNull _funLhsArgs
+isLhsFunctionLike FunctionLhs {..} = notNull (_funLhsTypeSig ^. typeSigArgs)
 
 isFunctionLike :: FunctionDef 'Parsed -> Bool
 isFunctionLike d@FunctionDef {..} =
diff --git a/src/Juvix/Compiler/Concrete/Language/Base.hs b/src/Juvix/Compiler/Concrete/Language/Base.hs
index ffcc6ab2de..6fbe2cc3b5 100644
--- a/src/Juvix/Compiler/Concrete/Language/Base.hs
+++ b/src/Juvix/Compiler/Concrete/Language/Base.hs
@@ -888,7 +888,7 @@ deriving stock instance Ord (RhsRecord 'Parsed)
 
 deriving stock instance Ord (RhsRecord 'Scoped)
 
-data RhsGadt (s :: Stage) = RhsGadt
+newtype RhsGadt (s :: Stage) = RhsGadt
   { _rhsGadtTypeSig :: TypeSig s
   }
   deriving stock (Generic)
@@ -3387,7 +3387,7 @@ instance (SingI s) => HasLoc (FunctionLhs s) where
     (getLoc <$> _funLhsBuiltin)
       ?<> (getLoc <$> _funLhsTerminating)
       ?<> ( getLocSymbolType _funLhsName
-              <>? (getLocExpressionType <$> _funLhsRetType)
+              <>? (getLocExpressionType <$> _funLhsTypeSig ^. typeSigRetType)
           )
 
 instance (SingI s) => HasLoc (FunctionDef s) where
diff --git a/src/Juvix/Compiler/Concrete/Translation/FromParsed/Analysis/Scoping.hs b/src/Juvix/Compiler/Concrete/Translation/FromParsed/Analysis/Scoping.hs
index 97bbd5fe28..05f48b38d3 100644
--- a/src/Juvix/Compiler/Concrete/Translation/FromParsed/Analysis/Scoping.hs
+++ b/src/Juvix/Compiler/Concrete/Translation/FromParsed/Analysis/Scoping.hs
@@ -1072,25 +1072,32 @@ checkDeriving ::
   Sem r (Deriving 'Scoped)
 checkDeriving Deriving {..} = do
   let lhs@FunctionLhs {..} = _derivingFunLhs
+      TypeSig {..} = _funLhsTypeSig
   (args', ret') <- withLocalScope $ do
-    args' <- mapM checkSigArg _funLhsArgs
-    ret' <- mapM checkParseExpressionAtoms _funLhsRetType
+    args' <- mapM checkSigArg _typeSigArgs
+    ret' <- mapM checkParseExpressionAtoms _typeSigRetType
     return (args', ret')
   name' <-
     if
         | P.isLhsFunctionLike lhs -> getReservedDefinitionSymbol _funLhsName
         | otherwise -> reserveFunctionSymbol lhs
-  let lhs' =
+  let typeSig' =
+        TypeSig
+          { _typeSigArgs = args',
+            _typeSigRetType = ret',
+            ..
+          }
+      lhs' =
         FunctionLhs
-          { _funLhsArgs = args',
-            _funLhsRetType = ret',
-            _funLhsName = name',
+          { _funLhsName = name',
+            _funLhsTypeSig = typeSig',
             ..
           }
   return
     Deriving
       { _derivingFunLhs = lhs',
-        ..
+        _derivingKw,
+        _derivingPragmas
       }
 
 checkSigArg ::
@@ -1156,6 +1163,16 @@ checkSigArgNames = \case
     ArgumentSymbol s -> ArgumentSymbol <$> bindVariableSymbol s
     ArgumentWildcard w -> return (ArgumentWildcard w)
 
+checkTypeSig ::
+  forall r.
+  (Members '[HighlightBuilder, Reader ScopeParameters, Error ScoperError, State Scope, State ScoperState, InfoTableBuilder, Reader InfoTable, NameIdGen, Reader PackageId, State ScoperSyntax, Reader BindingStrategy] r) =>
+  TypeSig 'Parsed ->
+  Sem r (TypeSig 'Scoped)
+checkTypeSig TypeSig {..} = do
+  a' <- mapM checkSigArg _typeSigArgs
+  t' <- mapM checkParseExpressionAtoms _typeSigRetType
+  return TypeSig {_typeSigArgs = a', _typeSigRetType = t', ..}
+
 checkFunctionDef ::
   forall r.
   (Members '[HighlightBuilder, Reader ScopeParameters, Error ScoperError, State Scope, State ScoperState, InfoTableBuilder, Reader InfoTable, NameIdGen, Reader PackageId, State ScoperSyntax, Reader BindingStrategy] r) =>
@@ -2194,11 +2211,16 @@ checkAxiomDef ::
   AxiomDef 'Parsed ->
   Sem r (AxiomDef 'Scoped)
 checkAxiomDef AxiomDef {..} = do
-  axiomType' <- withLocalScope (checkParseExpressionAtoms _axiomType)
   axiomName' <- getReservedDefinitionSymbol _axiomName
   axiomDoc' <- withLocalScope (mapM checkJudoc _axiomDoc)
   axiomSig' <- withLocalScope (checkTypeSig _axiomTypeSig)
-  let a = AxiomDef {_axiomName = axiomName', _axiomTypeSig = axiomSig', _axiomDoc = axiomDoc', ..}
+  let a =
+        AxiomDef
+          { _axiomName = axiomName',
+            _axiomTypeSig = axiomSig',
+            _axiomDoc = axiomDoc',
+            ..
+          }
   registerNameSignature (a ^. axiomName . S.nameId) a
   registerAxiom @$> a
 
diff --git a/src/Juvix/Compiler/Internal/Translation/FromConcrete.hs b/src/Juvix/Compiler/Internal/Translation/FromConcrete.hs
index 95e46588ce..aeed610f40 100644
--- a/src/Juvix/Compiler/Internal/Translation/FromConcrete.hs
+++ b/src/Juvix/Compiler/Internal/Translation/FromConcrete.hs
@@ -728,26 +728,18 @@ argToPattern arg@SigArg {..} = do
 
 goDefType ::
   forall r.
-  ( Members
-      '[ Reader DefaultArgsStack,
-         NameIdGen,
-         Error ScoperError,
-         Reader Pragmas,
-         Reader S.InfoTable
-       ]
-      r
-  ) =>
+  (Members '[Reader DefaultArgsStack, NameIdGen, Error ScoperError, Reader Pragmas, Reader S.InfoTable] r) =>
   FunctionLhs 'Scoped ->
   Sem r Internal.Expression
 goDefType FunctionLhs {..} = do
-  args <- concatMapM (fmap toList . argToParam) _funLhsArgs
-  ret <- maybe freshHole goExpression _funLhsRetType
+  args <- concatMapM (fmap toList . argToParam) (_funLhsTypeSig ^. typeSigArgs)
+  ret <- maybe freshHole goExpression (_funLhsTypeSig ^. typeSigRetType)
   return (Internal.foldFunType args ret)
   where
     freshHole :: Sem r Internal.Expression
     freshHole = do
       i <- freshNameId
-      let loc = maybe (getLoc _funLhsName) getLoc (lastMay _funLhsArgs)
+      let loc = maybe (getLoc _funLhsName) getLoc (lastMay (_funLhsTypeSig ^. typeSigArgs))
           h = mkHole loc i
       return $ Internal.ExpressionHole h
 
diff --git a/src/Juvix/Compiler/Pipeline/Package/Loader.hs b/src/Juvix/Compiler/Pipeline/Package/Loader.hs
index cc1a224bdd..38bff632ca 100644
--- a/src/Juvix/Compiler/Pipeline/Package/Loader.hs
+++ b/src/Juvix/Compiler/Pipeline/Package/Loader.hs
@@ -87,7 +87,8 @@ toConcrete t p = run . runReader l $ do
           _signTypeSig =
             TypeSig
               { _typeSigArgs = [],
-                ..
+                _typeSigRetType,
+                _typeSigColonKw
               }
       return
         ( StatementFunctionDef
@@ -98,11 +99,9 @@ toConcrete t p = run . runReader l $ do
                 _signDoc = Nothing,
                 _signCoercion = Nothing,
                 _signBuiltin = Nothing,
-                _signArgs = [],
-                _signRetType,
                 _signName,
-                _signColonKw,
-                _signBody
+                _signBody,
+                _signTypeSig
               }
         )