Elm compiler misleading error

Counter.elm

module Counter where

import Html exposing (..)
import Html.Attributes exposing (style)
import Html.Events exposing (onClick)

-- MODEL

type alias Model = Int


-- UPDATE

type Action = Increment | Decrement | Multiply Int | Zero | Mod Int | Round Int

update : Action -> Model -> Model
update action model =
    case action of
        Increment -> model + 1
        Decrement -> model - 1
        Multiply n -> model * n
        Zero -> 0
        Mod n -> model % n
        Round n -> (model // n) * n


-- VIEW

view : Signal.Address Action -> Model -> Html
view address model =
    body [
        style [
            ("font-family", "Ubuntu Mono, monospace")
            , ("font-size", "13px")
        ]
    ]
        [ div []
            [
            div [ countWrapper ] [
                -- XXX: Bad line
                h2 [ countStyle ] [ text (formatNumber (formatNumber model)) ]
                -- Correct line
                -- h2 [ countStyle ] [ text (formatNumber (toString model)) ]
                -- The following line is blamed instead
                , h2 [ countStyle ] [ text (toRadix' 2 model) ]
                , h2 [ countStyle ] [ text (toRadix' 8 model) ]
                , h2 [ countStyle ] [ text (toRadix' 12 model) ]
                , h2 [ countStyle ] [ text (toRadix' 16 model) ]
                , h2 [ countStyle ] [ text (toRadix' 36 model) ]
            ]
            , button [ buttonStyle, onClick address Decrement ] [ text "-" ]
            , button [ buttonStyle, onClick address Increment ] [ text "+" ]
            , button [ buttonStyle, onClick address (Multiply 2) ] [ text "×2" ]
            , button [ buttonStyle, onClick address Zero ] [ text "0" ]
            , button [ buttonStyle, onClick address (Mod 2) ] [ text "% 2" ]
            , button [ buttonStyle, onClick address (Round 2) ] [ text "_ 2" ]
            ]
        ]

countStyle : Attribute
countStyle = style
    [
    ("padding", "1em")
    , ("font-size", "200%")
    , ("color", "darkgrey")
    ]

countWrapper = style
    [
        ("display", "flex")
        , ("justify-content", "space-between")
        , ("flex-flow", "row wrap")
    ]

hoverHand = [ ("cursor", "pointer") ]
bold = [ ("font-weight", "bold") ]

buttonStyle =
    style
        ([ ("backgroundImage", "none")
        , ("border", "none")
        , ("backgroundColor", "darkgrey")
        , ("hover:backgroundColor", "black")
        , ("hover:color", "white")
        , ("text-transform", "capitalize")
        , ("padding", "12px 17px")
        ] ++ hoverHand ++ bold)

formatNumber : String -> String
formatNumber str =
    case str of
        "0" -> "0"
        n -> "et andet tal"

toRadix' : Int -> Int -> String
toRadix' n r = toString n

output.txt

TYPE MISMATCH
The 2nd argument to function `toRadix'` is causing a mismatch.

45|                 , h2 [ countStyle ] [ text (toRadix' 2 model) ]
Function `toRadix'` is expecting the 2nd argument to be:

    Int

But it is:

    String

Hint: I always figure out the type of arguments from left to right. If an
argument is acceptable when I check it, I assume it is "correct" in subsequent
checks. So the problem may actually be in how previous arguments interact with
the 2nd.