diff --git a/exercises/nucleotide-count/examples/success-standard/src/DNA.hs b/exercises/nucleotide-count/examples/success-standard/src/DNA.hs
index e1c30ce30..dac5e1d81 100644
--- a/exercises/nucleotide-count/examples/success-standard/src/DNA.hs
+++ b/exercises/nucleotide-count/examples/success-standard/src/DNA.hs
@@ -1,17 +1,21 @@
 {-# LANGUAGE TupleSections #-}
-
-module DNA (nucleotideCounts) where
+module DNA (nucleotideCounts, Nucleotide(..)) where
 
 import Data.Map.Strict (Map, fromDistinctAscList, fromListWith, findWithDefault)
 
-nucleotideCounts :: String -> Either String (Map Char Int)
-nucleotideCounts xs = fromDistinctAscList <$> mapM count' "ACGT"
+data Nucleotide = A | C | G | T deriving (Eq, Ord, Show)
+
+nucleotideCounts :: String -> Either String (Map Nucleotide Int)
+nucleotideCounts xs = fromDistinctAscList <$> mapM count' [A,C,G,T]
   where
     count' x = (x,) <$> occur' x
     occur' x = findWithDefault 0 x . countOccurrences <$> mapM valid xs
     countOccurrences = fromListWith (+) . flip zip (repeat 1)
 
-valid :: Char -> Either String Char
-valid x
-  | x `elem` "ACGT" = Right x
-  | otherwise       = Left $ "invalid nucleotide " ++ show x
+valid :: Char -> Either String Nucleotide
+valid c = case c of
+  'A' -> Right A
+  'C' -> Right C
+  'G' -> Right G
+  'T' -> Right T
+  _   -> Left $ "Invalid nucleotide " ++ show c
diff --git a/exercises/nucleotide-count/package.yaml b/exercises/nucleotide-count/package.yaml
index 6263f9121..3de1f22a5 100644
--- a/exercises/nucleotide-count/package.yaml
+++ b/exercises/nucleotide-count/package.yaml
@@ -1,5 +1,5 @@
 name: nucleotide-count
-version: 1.3.0.5
+version: 1.3.0.6
 
 dependencies:
   - base
diff --git a/exercises/nucleotide-count/src/DNA.hs b/exercises/nucleotide-count/src/DNA.hs
index 4dd7811f5..d82efd5b3 100644
--- a/exercises/nucleotide-count/src/DNA.hs
+++ b/exercises/nucleotide-count/src/DNA.hs
@@ -1,6 +1,8 @@
-module DNA (nucleotideCounts) where
+module DNA (nucleotideCounts, Nucleotide(..)) where
 
 import Data.Map (Map)
 
-nucleotideCounts :: String -> Either String (Map Char Int)
+data Nucleotide = A | C | G | T deriving (Eq, Ord, Show)
+
+nucleotideCounts :: String -> Either String (Map Nucleotide Int)
 nucleotideCounts xs = error "You need to implement this function."
diff --git a/exercises/nucleotide-count/test/Tests.hs b/exercises/nucleotide-count/test/Tests.hs
index 33620b414..07fb67975 100644
--- a/exercises/nucleotide-count/test/Tests.hs
+++ b/exercises/nucleotide-count/test/Tests.hs
@@ -5,7 +5,7 @@ import Data.Map          (fromList)
 import Test.Hspec        (Spec, describe, it, shouldBe, shouldSatisfy)
 import Test.Hspec.Runner (configFastFail, defaultConfig, hspecWith)
 
-import DNA (nucleotideCounts)
+import DNA (nucleotideCounts, Nucleotide(..))
 
 main :: IO ()
 main = hspecWith defaultConfig {configFastFail = True} specs
@@ -18,29 +18,29 @@ specs = do
           describe "nucleotideCounts" $ do
 
             it "empty dna strand has no nucleotides" $
-              nucleotideCounts "" `matchesMap` [ ('A', 0)
-                                               , ('C', 0)
-                                               , ('G', 0)
-                                               , ('T', 0) ]
+              nucleotideCounts "" `matchesMap` [ (A, 0)
+                                               , (C, 0)
+                                               , (G, 0)
+                                               , (T, 0) ]
 
             it "can count one nucleotide in single-character input" $
-              nucleotideCounts "G" `matchesMap` [ ('A', 0)
-                                                , ('C', 0)
-                                                , ('G', 1)
-                                                , ('T', 0) ]
+              nucleotideCounts "G" `matchesMap` [ (A, 0)
+                                                , (C, 0)
+                                                , (G, 1)
+                                                , (T, 0) ]
 
             it "repetitive-sequence-has-only-guanosine" $
-              nucleotideCounts "GGGGGGGG" `matchesMap` [ ('A', 0)
-                                                       , ('C', 0)
-                                                       , ('G', 8)
-                                                       , ('T', 0) ]
+              nucleotideCounts "GGGGGGGG" `matchesMap` [ (A, 0)
+                                                       , (C, 0)
+                                                       , (G, 8)
+                                                       , (T, 0) ]
 
             it "counts all nucleotides" $
               nucleotideCounts "AGCTTTTCATTCTGACTGCAACGGGCAATATGTCTCTGTGTGGATTAAAAAAAGAGTGTCTGATAGCAGC"
-              `matchesMap` [ ('A', 20)
-                           , ('C', 12)
-                           , ('G', 17)
-                           , ('T', 21) ]
+              `matchesMap` [ (A, 20)
+                           , (C, 12)
+                           , (G, 17)
+                           , (T, 21) ]
 
             it "validates strand" $
               nucleotideCounts "AGXXACT" `shouldSatisfy` isLeft