diff --git a/exercises/phone-number/PhoneNumber.example b/exercises/phone-number/PhoneNumber.example
index df545b5..c5271a3 100644
--- a/exercises/phone-number/PhoneNumber.example
+++ b/exercises/phone-number/PhoneNumber.example
@@ -2,23 +2,43 @@ module PhoneNumber (..) where
 
 import String
 
-nums = ['1','2','3','4','5','6','7','8','9','0']
 
-getNumber : String -> String
-getNumber text = getValidNum (String.filter isDigit text)
+nums =
+  [ '1', '2', '3', '4', '5', '6', '7', '8', '9', '0' ]
+
+
+getNumber : String -> Maybe String
+getNumber text =
+  getValidNum (String.filter isDigit text)
+
 
 isDigit : Char -> Bool
-isDigit char = List.any (\n -> n == char) nums
+isDigit char =
+  List.any (\n -> n == char) nums
 
-getValidNum : String -> String
+
+getValidNum : String -> Maybe String
 getValidNum num =
-  if String.length num == 10 then num else
-    if (String.length num == 11) && (String.left 1 num == "1") then String.dropLeft 1 num else
-      String.repeat 10 "0"
+  if String.length num == 10 then
+    Just num
+  else if (String.length num == 11) && (String.left 1 num == "1") then
+    Just (String.dropLeft 1 num)
+  else
+    Nothing
 
-printPretty : String -> String
-printPretty input = formatNumber (getNumber input)
+
+prettyPrint : String -> Maybe String
+prettyPrint input =
+  Maybe.map formatNumber (getNumber input)
 
 
 formatNumber : String -> String
-formatNumber input = String.concat ["(", (String.slice 0 3 input),  ") ", (String.slice 3 6 input), "-", (String.slice 6 10 input)]
+formatNumber input =
+  String.concat
+    [ "("
+    , (String.slice 0 3 input)
+    , ") "
+    , (String.slice 3 6 input)
+    , "-"
+    , (String.slice 6 10 input)
+    ]
diff --git a/exercises/phone-number/PhoneNumberTests.elm b/exercises/phone-number/PhoneNumberTests.elm
index c0af62b..1a116dd 100644
--- a/exercises/phone-number/PhoneNumberTests.elm
+++ b/exercises/phone-number/PhoneNumberTests.elm
@@ -3,7 +3,7 @@ module Main (..) where
 import Task
 import Console
 import ElmTest exposing (..)
-import PhoneNumber exposing (getNumber, printPretty)
+import PhoneNumber exposing (getNumber, prettyPrint)
 
 
 tests : Test
@@ -12,40 +12,40 @@ tests =
     "PhoneNumber"
     [ test
         "cleans number"
-        (assertEqual "1234567890" (getNumber "(123) 456-7890"))
+        (assertEqual (Just "1234567890") (getNumber "(123) 456-7890"))
     , test
         "cleans number with dots"
-        (assertEqual "1234567890" (getNumber "123.456.7890"))
+        (assertEqual (Just "1234567890") (getNumber "123.456.7890"))
     , test
         "valid when 11 digits and first is 1"
-        (assertEqual "1234567890" (getNumber "11234567890"))
+        (assertEqual (Just "1234567890") (getNumber "11234567890"))
     , test
         "invalid when 11 digits"
-        (assertEqual "0000000000" (getNumber "21234567890"))
+        (assertEqual Nothing (getNumber "21234567890"))
     , test
         "invalid when 9 digits"
-        (assertEqual "0000000000" (getNumber "123456789"))
+        (assertEqual Nothing (getNumber "123456789"))
     , test
         "invalid when 12 digits"
-        (assertEqual "0000000000" (getNumber "123456789012"))
+        (assertEqual Nothing (getNumber "123456789012"))
     , test
         "invalid when empty"
-        (assertEqual "0000000000" (getNumber ""))
+        (assertEqual Nothing (getNumber ""))
     , test
         "invalid when no digits present"
-        (assertEqual "0000000000" (getNumber " (-) "))
+        (assertEqual Nothing (getNumber " (-) "))
     , test
         "valid with leading characters"
-        (assertEqual "1234567890" (getNumber "my number is 123 456 7890"))
+        (assertEqual (Just "1234567890") (getNumber "my number is 123 456 7890"))
     , test
         "valid with trailing characters"
-        (assertEqual "1234567890" (getNumber "123 456 7890 - bob"))
+        (assertEqual (Just "1234567890") (getNumber "123 456 7890 - bob"))
     , test
         "pretty print"
-        (assertEqual "(123) 456-7890" (printPretty "1234567890"))
+        (assertEqual (Just "(123) 456-7890") (prettyPrint "1234567890"))
     , test
         "pretty print with full us phone number"
-        (assertEqual "(123) 456-7890" (printPretty "11234567890"))
+        (assertEqual (Just "(123) 456-7890") (prettyPrint "11234567890"))
     ]