diff --git a/src/Yesod/Form/Bootstrap4.hs b/src/Yesod/Form/Bootstrap4.hs
--- a/src/Yesod/Form/Bootstrap4.hs
+++ b/src/Yesod/Form/Bootstrap4.hs
@@ -7,18 +7,18 @@
 -- yesod-form under MIT license, author is Michael Snoyman <michael@snoyman.com>
 
 module Yesod.Form.Bootstrap4
-    ( renderBootstrap4
-    , BootstrapFormLayout(..)
-    , BootstrapGridOptions(..)
-    , bfs
-    , withPlaceholder
-    , withAutofocus
-    , withLargeInput
-    , withSmallInput
-    , bootstrapSubmit
-    , mbootstrapSubmit
-    , BootstrapSubmit(..)
-    ) where
+  ( renderBootstrap4
+  , BootstrapFormLayout(..)
+  , BootstrapGridOptions(..)
+  , bfs
+  , withPlaceholder
+  , withAutofocus
+  , withLargeInput
+  , withSmallInput
+  , bootstrapSubmit
+  , mbootstrapSubmit
+  , BootstrapSubmit(..)
+  ) where
 
 import           Control.Arrow (second)
 import           Data.Maybe    (isJust)
@@ -33,25 +33,25 @@
 
 withPlaceholder :: Text -> FieldSettings site -> FieldSettings site
 withPlaceholder placeholder fs = fs { fsAttrs = newAttrs }
-    where newAttrs = ("placeholder", placeholder) : fsAttrs fs
+  where newAttrs = ("placeholder", placeholder) : fsAttrs fs
 
 -- | Add an autofocus attribute to a field.
 withAutofocus :: FieldSettings site -> FieldSettings site
 withAutofocus fs = fs { fsAttrs = newAttrs }
-    where newAttrs = ("autofocus", "autofocus") : fsAttrs fs
+  where newAttrs = ("autofocus", "autofocus") : fsAttrs fs
 
 -- | Add the @input-lg@ CSS class to a field.
 withLargeInput :: FieldSettings site -> FieldSettings site
 withLargeInput fs = fs { fsAttrs = newAttrs }
-    where newAttrs = addClass "form-control-lg" (fsAttrs fs)
+  where newAttrs = addClass "form-control-lg" (fsAttrs fs)
 
 -- | Add the @input-sm@ CSS class to a field.
 withSmallInput :: FieldSettings site -> FieldSettings site
 withSmallInput fs = fs { fsAttrs = newAttrs }
-    where newAttrs = addClass "form-control-sm" (fsAttrs fs)
+  where newAttrs = addClass "form-control-sm" (fsAttrs fs)
 
 data BootstrapGridOptions = ColXs !Int | ColSm !Int | ColMd !Int | ColLg !Int | ColXl !Int
-    deriving (Eq, Ord, Show, Read)
+  deriving (Eq, Ord, Show, Read)
 
 toColumn :: BootstrapGridOptions -> String
 toColumn (ColXs columns) = "col-xs-" ++ show columns
@@ -76,89 +76,88 @@
 addGO (ColXs a) other     = addGO (ColSm a) other
 addGO (ColSm a) other     = addGO (ColMd a) other
 addGO (ColMd a) other     = addGO (ColLg a) other
-addGO _         _         = error "Yesod.Form.Bootstrap.addGO: never here"
+addGO _     _             = error "Yesod.Form.Bootstrap.addGO: never here"
 
 -- | The layout used for the bootstrap form.
 data BootstrapFormLayout = BootstrapBasicForm | BootstrapInlineForm |
-    BootstrapHorizontalForm
-    { bflLabelOffset :: !BootstrapGridOptions
-    , bflLabelSize   :: !BootstrapGridOptions
-    , bflInputOffset :: !BootstrapGridOptions
-    , bflInputSize   :: !BootstrapGridOptions
-    }
-    deriving (Eq, Ord, Show, Read)
+  BootstrapHorizontalForm
+  { bflLabelOffset :: !BootstrapGridOptions
+  , bflLabelSize   :: !BootstrapGridOptions
+  , bflInputOffset :: !BootstrapGridOptions
+  , bflInputSize   :: !BootstrapGridOptions
+  }
+  deriving (Eq, Ord, Show, Read)
 
 -- | Render the given form using Bootstrap v3 conventions.
 renderBootstrap4 :: Monad m => BootstrapFormLayout -> FormRender m a
 renderBootstrap4 formLayout aform fragment = do
-    (res, views') <- aFormToForm aform
-    let views = views' []
-        widget = [whamlet|
-            #{fragment}
-            $forall view <- views
-              <div .form-group :isJust (fvErrors view):.has-danger>
-                $case formLayout
-                  $of BootstrapBasicForm
-                    $if fvId view /= bootstrapSubmitId
-                      <label .form-control-label for=#{fvId view}>#{fvLabel view}
-                    ^{fvInput view}
-                    ^{helpWidget view}
-                  $of BootstrapInlineForm
-                    $if fvId view /= bootstrapSubmitId
-                      <label .sr-only .form-control-label for=#{fvId view}>#{fvLabel view}
-                    ^{fvInput view}
-                    ^{helpWidget view}
-                  $of BootstrapHorizontalForm labelOffset labelSize inputOffset inputSize
-                    $if fvId view /= bootstrapSubmitId
-                      <div .row>
-                        <label
-                          .form-control-label
-                          .#{toOffset labelOffset}
-                          .#{toColumn labelSize}
-                          for=#{fvId view}>#{fvLabel view}
-                        <div .#{toOffset inputOffset} .#{toColumn inputSize}>
-                          ^{fvInput view}
-                          ^{helpWidget view}
-                    $else
-                      <div
-                        .#{toOffset (addGO inputOffset (addGO labelOffset labelSize))}
-                        .#{toColumn inputSize}>
-                        ^{fvInput view}
-                        ^{helpWidget view}
-                |]
-    return (res, widget)
+  (res, views') <- aFormToForm aform
+  let views = views' []
+      widget = [whamlet|
+#{fragment}
+$forall view <- views
+  <div .form-group :isJust (fvErrors view):.has-danger>
+    $case formLayout
+      $of BootstrapBasicForm
+        $if fvId view /= bootstrapSubmitId
+          <label for=#{fvId view}>#{fvLabel view}
+        ^{fvInput view}
+        ^{helpWidget view}
+      $of BootstrapInlineForm
+        $if fvId view /= bootstrapSubmitId
+          <label .sr-only for=#{fvId view}>#{fvLabel view}
+        ^{fvInput view}
+        ^{helpWidget view}
+      $of BootstrapHorizontalForm labelOffset labelSize inputOffset inputSize
+        $if fvId view /= bootstrapSubmitId
+          <div .row>
+            <label
+              .#{toOffset labelOffset}
+              .#{toColumn labelSize}
+              for=#{fvId view}>#{fvLabel view}
+            <div .#{toOffset inputOffset} .#{toColumn inputSize}>
+              ^{fvInput view}
+              ^{helpWidget view}
+        $else
+          <div
+            .#{toOffset (addGO inputOffset (addGO labelOffset labelSize))}
+            .#{toColumn inputSize}>
+            ^{fvInput view}
+            ^{helpWidget view}
+    |]
+  return (res, widget)
 
 -- | (Internal) Render a help widget for tooltips and errors.
 helpWidget :: FieldView site -> WidgetFor site ()
 helpWidget view = [whamlet|
-    $maybe err <- fvErrors view
-      <div .form-control-feedback>#{err}
-    $maybe tt <- fvTooltip view
-      <small .form-text .text-muted>#{tt}
+$maybe err <- fvErrors view
+  <div .invalid-feedback>#{err}
+$maybe tt <- fvTooltip view
+  <small .form-text .text-muted>#{tt}
 |]
 
 -- | How the 'bootstrapSubmit' button should be rendered.
 data BootstrapSubmit msg =
-    BootstrapSubmit
-    { bsValue   :: msg -- ^ The text of the submit button.
-    , bsClasses :: Text -- ^ Classes added to the @\<button>@.
-    , bsAttrs   :: [(Text, Text)] -- ^ Attributes added to the @\<button>@.
-    } deriving (Eq, Ord, Show, Read)
+  BootstrapSubmit
+  { bsValue   :: msg -- ^ The text of the submit button.
+  , bsClasses :: Text -- ^ Classes added to the @\<button>@.
+  , bsAttrs   :: [(Text, Text)] -- ^ Attributes added to the @\<button>@.
+  } deriving (Eq, Ord, Show, Read)
 
 instance IsString msg => IsString (BootstrapSubmit msg) where
-    fromString msg = BootstrapSubmit (fromString msg) "btn-primary" []
+  fromString msg = BootstrapSubmit (fromString msg) "btn-primary" []
 
 -- | A Bootstrap v4 submit button disguised as a field for
 -- convenience.  For example, if your form currently is:
 --
--- > Person <$> areq textField "Name"    Nothing
--- >        <*> areq textField "Surname" Nothing
+-- > Person <$> areq textField "Name"  Nothing
+-- >    <*> areq textField "Surname" Nothing
 --
 -- Then just change it to:
 --
--- > Person <$> areq textField "Name"    Nothing
--- >        <*> areq textField "Surname" Nothing
--- >        <*  bootstrapSubmit ("Register" :: BootstrapSubmit Text)
+-- > Person <$> areq textField "Name"  Nothing
+-- >    <*> areq textField "Surname" Nothing
+-- >    <*  bootstrapSubmit ("Register" :: BootstrapSubmit Text)
 --
 -- (Note that '<*' is not a typo.)
 --
@@ -166,24 +165,26 @@
 -- manually as well in order to have more control over its
 -- layout.
 bootstrapSubmit :: (RenderMessage site msg, HandlerSite m ~ site, MonadHandler m) =>
-    BootstrapSubmit msg -> AForm m ()
+  BootstrapSubmit msg -> AForm m ()
 bootstrapSubmit = formToAForm . fmap (second return) . mbootstrapSubmit
 
 -- | Same as 'bootstrapSubmit' but for monadic forms.  This isn't
 -- as useful since you're not going to use 'renderBootstrap4'
 -- anyway.
 mbootstrapSubmit :: (RenderMessage site msg, HandlerSite m ~ site, MonadHandler m) =>
-    BootstrapSubmit msg -> MForm m (FormResult (), FieldView site)
+  BootstrapSubmit msg -> MForm m (FormResult (), FieldView site)
 mbootstrapSubmit (BootstrapSubmit msg classes attrs) =
-    let res = FormSuccess ()
-        widget = [whamlet|<button class="btn #{classes}" type=submit *{attrs}>_{msg}|]
-        fv  = FieldView { fvLabel    = ""
-                        , fvTooltip  = Nothing
-                        , fvId       = bootstrapSubmitId
-                        , fvInput    = widget
-                        , fvErrors   = Nothing
-                        , fvRequired = False }
-    in return (res, fv)
+  let res = FormSuccess ()
+      widget = [whamlet|<button class="btn #{classes}" type=submit *{attrs}>_{msg}|]
+      fv  = FieldView
+            { fvLabel    = ""
+            , fvTooltip  = Nothing
+            , fvId       = bootstrapSubmitId
+            , fvInput    = widget
+            , fvErrors   = Nothing
+            , fvRequired = False
+            }
+  in return (res, fv)
 
 -- | A royal hack.  Magic id used to identify whether a field
 -- should have no label.  A valid HTML4 id which is probably not
diff --git a/yesod-form-bootstrap4.cabal b/yesod-form-bootstrap4.cabal
--- a/yesod-form-bootstrap4.cabal
+++ b/yesod-form-bootstrap4.cabal
@@ -2,10 +2,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: e6da7e86970590a4b47e6c1d2d466868a14ed599969f7b55c017f64fd5dad8b6
+-- hash: 394ee8edcbb802cb7628af29db1bb090b6fc8682b129dd772eaa73a32e5e4ee5
 
 name:           yesod-form-bootstrap4
-version:        1.0.2
+version:        2.0.0
 synopsis:       renderBootstrap4
 category:       Web
 homepage:       https://github.com/ncaq/yesod-form-bootstrap4#readme