diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,11 @@
 
 ## Unreleased changes
 
+## 0.1.3.0
+
+- Added support `where` clause [#11](https://github.com/waddlaw/haskell-stack-trace-plugin/pull/11) (@waddlaw)
+- Avoid redundant-constraints warnings [#12](https://github.com/waddlaw/haskell-stack-trace-plugin/pull/12) (@waddlaw)
+
 ## 0.1.2.0 -- 2021-05-21
 
 - Added support for GHC 8.10 [#7](https://github.com/waddlaw/haskell-stack-trace-plugin/pull/7) (@etorreborre)
diff --git a/Readme.md b/Readme.md
--- a/Readme.md
+++ b/Readme.md
@@ -32,10 +32,10 @@
 
 -- HsQualTy
 f4 :: Show a => a -> Int
-f4 _ = f5 0 0
+f4 n = f5 (show n) 0
 
 -- HsFunTy
-f5 :: Int -> Int -> Int
+f5 :: String -> Int -> Int
 f5 _ _ = head f6
 
 -- HsListTy
@@ -48,8 +48,14 @@
 
 -- HsAppTy
 f8 :: Maybe Int
-f8 = Just fError
+f8 = Just f9
 
+f9 :: Int
+f9 = f10
+  where
+    f10 :: Int
+    f10 = fError
+
 -- HsTyVar
 fError :: Int
 fError = error "fError"
@@ -58,7 +64,7 @@
 This example get error:
 
 ```shell
-$ cabal new-build
+$ cabal build
 example/Main.hs:15:7: error:
     Not in scope: type constructor or class ‘HasCallStack’
    |
@@ -71,10 +77,10 @@
 Fix and rebuild!
 
 ```shell
-$ cabal new-run
+$ cabal run example -v0
 example: fError
 CallStack (from HasCallStack):
-  error, called at example/Main.hs:41:10 in main:Main
+  error, called at example/Main.hs:47:10 in main:Main
 ```
 
 Hmm, it is not useful. But, you will to be happy when enable this plugin.
@@ -85,22 +91,22 @@
 ```
 
 ```shell
-$ cabal new-run
-...
-
+$ cabal run example -v0
 example: fError
 CallStack (from HasCallStack):
-  error, called at example/Main.hs:40:10 in main:Main
-  fError, called at example/Main.hs:36:11 in main:Main
-  f8, called at example/Main.hs:32:16 in main:Main
-  f7, called at example/Main.hs:28:11 in main:Main
-  f6, called at example/Main.hs:24:15 in main:Main
-  f5, called at example/Main.hs:20:8 in main:Main
-  f4, called at example/Main.hs:16:6 in main:Main
-  f3, called at example/Main.hs:12:6 in main:Main
-  f2, called at example/Main.hs:9:6 in main:Main
-  f1, called at example/Main.hs:6:14 in main:Main
-  main, called at example/Main.hs:6:1 in main:Main
+  error, called at example/Main.hs:47:10 in main:Main
+  fError, called at example/Main.hs:43:11 in main:Main
+  f10, called at example/Main.hs:40:6 in main:Main
+  f9, called at example/Main.hs:37:11 in main:Main
+  f8, called at example/Main.hs:33:16 in main:Main
+  f7, called at example/Main.hs:29:11 in main:Main
+  f6, called at example/Main.hs:25:15 in main:Main
+  f5, called at example/Main.hs:21:8 in main:Main
+  f4, called at example/Main.hs:17:6 in main:Main
+  f3, called at example/Main.hs:13:6 in main:Main
+  f2, called at example/Main.hs:10:6 in main:Main
+  f1, called at example/Main.hs:7:14 in main:Main
+  main, called at example/Main.hs:7:1 in main:Main
 ```
 
 Great!!!
diff --git a/example/Main.hs b/example/Main.hs
--- a/example/Main.hs
+++ b/example/Main.hs
@@ -18,10 +18,10 @@
 
 -- HsQualTy
 f4 :: Show a => a -> Int
-f4 _ = f5 0 0
+f4 n = f5 (show n) 0
 
 -- HsFunTy
-f5 :: Int -> Int -> Int
+f5 :: String -> Int -> Int
 f5 _ _ = head f6
 
 -- HsListTy
@@ -34,7 +34,13 @@
 
 -- HsAppTy
 f8 :: Maybe Int
-f8 = Just fError
+f8 = Just f9
+
+f9 :: Int
+f9 = f10
+  where
+    f10 :: Int
+    f10 = fError
 
 -- HsTyVar
 fError :: Int
diff --git a/haskell-stack-trace-plugin.cabal b/haskell-stack-trace-plugin.cabal
--- a/haskell-stack-trace-plugin.cabal
+++ b/haskell-stack-trace-plugin.cabal
@@ -1,6 +1,6 @@
 cabal-version:      2.4
 name:               haskell-stack-trace-plugin
-version:            0.1.2.0
+version:            0.1.3.0
 synopsis:           haskell-stack-trace-plugin
 description:
   This plugin allow implicitly add HasCallStack class to every top-level function for all module. Hence, we can to get completely continuous call stack.
@@ -72,5 +72,5 @@
   import:         common-opts
   main-is:        Main.hs
   hs-source-dirs: example
-  ghc-options:    -fplugin=StackTrace.Plugin
+  ghc-options:    -fplugin=StackTrace.Plugin -Wredundant-constraints
   build-depends:  haskell-stack-trace-plugin
diff --git a/src/StackTrace/Plugin.hs b/src/StackTrace/Plugin.hs
--- a/src/StackTrace/Plugin.hs
+++ b/src/StackTrace/Plugin.hs
@@ -79,7 +79,6 @@
     astTraversal :: Traversal' (LHsDecl GhcPs) (HsType GhcPs)
     astTraversal = updateHsmodDecl
                  . updateHsDecl
-                 . updateSig
                  . updateLHsSigWsType
                  . updateLHsSigType
                  . updateLHsType
@@ -88,10 +87,56 @@
 updateHsmodDecl :: Traversal' (LHsDecl GhcPs) (HsDecl GhcPs)
 updateHsmodDecl = traverse
 
-updateHsDecl :: Traversal' (HsDecl GhcPs) (Sig GhcPs)
-updateHsDecl f (SigD xSig s) = SigD xSig <$> f s
+updateHsDecl :: Traversal' (HsDecl GhcPs) (LHsSigWcType GhcPs)
+updateHsDecl f (SigD xSig s) = SigD xSig <$> updateSig f s
+updateHsDecl f (ValD xVal hsBind) = ValD xVal <$> updateHsBind f hsBind
 updateHsDecl _ sig = pure sig
 
+updateHsBind :: Traversal' (HsBind GhcPs) (LHsSigWcType GhcPs)
+updateHsBind f bind@FunBind {} = (\x -> bind {fun_matches = x}) <$> updateMatchGroup f (fun_matches bind)
+updateHsBind _ bind = pure bind
+
+updateMatchGroup :: Traversal' (MatchGroup GhcPs (LHsExpr GhcPs)) (LHsSigWcType GhcPs)
+updateMatchGroup f mg@MG {} = (\x -> mg {mg_alts = x}) <$> updateLLMatch f (mg_alts mg)
+#if __GLASGOW_HASKELL__ < 900
+updateMatchGroup _ mg = pure mg
+#endif
+
+updateLocated :: Functor f => (a -> b -> f c) -> a -> Located b -> f (Located c)
+updateLocated f g (L l e) = L l <$> f g e
+
+updateLLMatch :: Traversal' (Located [LMatch GhcPs (LHsExpr GhcPs)]) (LHsSigWcType GhcPs)
+updateLLMatch = updateLocated updateLMatches
+
+updateLMatches :: Traversal' [LMatch GhcPs (LHsExpr GhcPs)] (LHsSigWcType GhcPs)
+updateLMatches f = traverse (updateLocated updateMatch f)
+
+updateMatch :: Traversal' (Match GhcPs (LHsExpr GhcPs)) (LHsSigWcType GhcPs)
+updateMatch f m@Match {} = (\x -> m {m_grhss = x}) <$> updateGrhss f (m_grhss m)
+#if __GLASGOW_HASKELL__ < 900
+updateMatch _ m = pure m
+#endif
+
+updateGrhss :: Traversal' (GRHSs GhcPs (LHsExpr GhcPs)) (LHsSigWcType GhcPs)
+updateGrhss f grhss@GRHSs {} = (\x -> grhss {grhssLocalBinds = x}) <$> updateLHsLocalBinds f (grhssLocalBinds grhss)
+#if __GLASGOW_HASKELL__ < 900
+updateGrhss _ grhss = pure grhss
+#endif
+
+updateLHsLocalBinds :: Traversal' (LHsLocalBinds GhcPs) (LHsSigWcType GhcPs)
+updateLHsLocalBinds = updateLocated updateLocalBinds
+
+updateLocalBinds :: Traversal' (HsLocalBinds GhcPs) (LHsSigWcType GhcPs)
+updateLocalBinds f (HsValBinds xHsValBinds hsValBindsLR) = HsValBinds xHsValBinds <$> updateHsValBindsLR f hsValBindsLR
+updateLocalBinds _ hsValBinds = pure hsValBinds
+
+updateHsValBindsLR :: Traversal' (HsValBindsLR GhcPs GhcPs) (LHsSigWcType GhcPs)
+updateHsValBindsLR f (ValBinds xValBinds lHsBindsLR lSigs) = ValBinds xValBinds lHsBindsLR <$> updateLSigs f lSigs
+updateHsValBindsLR _ valBinds = pure valBinds
+
+updateLSigs :: Traversal' [LSig GhcPs] (LHsSigWcType GhcPs)
+updateLSigs f = traverse (updateLocated updateSig f)
+
 updateSig :: Traversal' (Sig GhcPs) (LHsSigWcType GhcPs)
 updateSig f (TypeSig xSig ls t) = TypeSig xSig ls <$> f t
 updateSig _ sig = pure sig
@@ -115,15 +160,17 @@
 
 -- Main process
 updateHsType :: HsType GhcPs -> (Any, HsType GhcPs)
-updateHsType (HsQualTy xty ctxt body) =
-  flagASTModified $ HsQualTy xty (fmap appendHSC ctxt) body
+updateHsType ty@(HsQualTy xty ctxt body) =
+  if hasHasCallStack (unLoc ctxt)
+    then pure ty
+    else flagASTModified $ HsQualTy xty (fmap appendHSC ctxt) body
 updateHsType ty@HsTyVar {} =
   flagASTModified $ HsQualTy xQualTy (noLoc $ appendHSC []) (noLoc ty)
 updateHsType ty@HsAppTy {} =
   flagASTModified $ HsQualTy xQualTy (noLoc $ appendHSC []) (noLoc ty)
 updateHsType ty@HsFunTy {} =
   flagASTModified $ HsQualTy xQualTy (noLoc $ appendHSC []) (noLoc ty)
-updateHsType ty@HsListTy {} =
+updateHsType ty@HsListTy {} = 
   flagASTModified $ HsQualTy xQualTy (noLoc $ appendHSC []) (noLoc ty)
 updateHsType ty@HsTupleTy {} =
   flagASTModified $ HsQualTy xQualTy (noLoc $ appendHSC []) (noLoc ty)
@@ -142,6 +189,13 @@
 
 appendHSC :: HsContext GhcPs -> HsContext GhcPs
 appendHSC cs = mkHSC : cs
+
+hasHasCallStack :: HsContext GhcPs -> Bool
+hasHasCallStack = any (checkHsType . unLoc)
+  where
+    checkHsType :: HsType GhcPs -> Bool
+    checkHsType (HsTyVar _ _ lid) = unLoc lid == (mkRdrUnqual $ mkClsOcc  "HasCallStack")
+    checkHsType _ = False
 
 -- make HasCallStack => constraint
 mkHSC :: LHsType GhcPs