diff --git a/CHANGES.txt b/CHANGES.txt
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,5 +1,7 @@
 Changelog for HLint
 
+1.9.28
+    #215, spot newtype deriving inside classes
 1.9.27
     #203, avoid recompiling everything twice
     #213, don't suggest removing bang patterns on let
diff --git a/hlint.cabal b/hlint.cabal
--- a/hlint.cabal
+++ b/hlint.cabal
@@ -1,7 +1,7 @@
 cabal-version:      >= 1.8
 build-type:         Simple
 name:               hlint
-version:            1.9.27
+version:            1.9.28
 license:            BSD3
 license-file:       LICENSE
 category:           Development
diff --git a/src/Hint/Extensions.hs b/src/Hint/Extensions.hs
--- a/src/Hint/Extensions.hs
+++ b/src/Hint/Extensions.hs
@@ -59,6 +59,8 @@
 deriving instance Show Bar -- {-# LANGUAGE StandaloneDeriving #-}
 {-# LANGUAGE DeriveGeneric, GeneralizedNewtypeDeriving #-} \
 newtype Micro = Micro Int deriving Generic -- {-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-} \
+instance Class Int where {newtype MyIO a = MyIO a deriving NewClass}
 {-# LANGUAGE UnboxedTuples #-} \
 f :: Int -> (# Int, Int #)
 {-# LANGUAGE UnboxedTuples #-} \
@@ -172,16 +174,21 @@
 -- | What is derived on newtype, and on data type
 --   'deriving' declarations may be on either, so we approximate as both newtype and data
 derives :: Module_ -> ([String],[String])
-derives = concatUnzip . map f . childrenBi
+derives m = concatUnzip $ map decl (childrenBi m) ++ map idecl (childrenBi m)
     where
-        f :: Decl_ -> ([String], [String])
-        f (DataDecl _ dn _ _ _ ds) = g dn ds
-        f (GDataDecl _ dn _ _ _ _ ds) = g dn ds
-        f (DataInsDecl _ dn _ _ ds) = g dn ds
-        f (GDataInsDecl _ dn _ _ _ ds) = g dn ds
-        f (DerivDecl _ _ hd) = (xs, xs) -- don't know whether this was on newtype or not
+        idecl :: InstDecl S -> ([String], [String])
+        idecl (InsData _ dn _ _ ds) = g dn ds
+        idecl (InsGData _ dn _ _ _ ds) = g dn ds
+        idecl _ = ([], [])
+
+        decl :: Decl_ -> ([String], [String])
+        decl (DataDecl _ dn _ _ _ ds) = g dn ds
+        decl (GDataDecl _ dn _ _ _ _ ds) = g dn ds
+        decl (DataInsDecl _ dn _ _ ds) = g dn ds
+        decl (GDataInsDecl _ dn _ _ _ ds) = g dn ds
+        decl (DerivDecl _ _ hd) = (xs, xs) -- don't know whether this was on newtype or not
             where xs = [ir hd]
-        f _ = ([], [])
+        decl _ = ([], [])
 
         g dn ds = if isNewType dn then (xs,[]) else ([],xs)
             where xs = maybe [] (map ir . fromDeriving) ds