diff --git a/CHANGES.rst b/CHANGES.rst
index 5a4f49890..23d86fc43 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -26,6 +26,8 @@ Unreleased
 -   Choices shortcut for :class:`~fields.core.SelectMultipleField`.
     :issue:`603` :pr:`605`
 -   Forms can have form-level errors. :issue:`55` :pr:`595`
+-   Fixed a bug related to `for` and `class` html parameter rendering.
+    :issue:`449` :pr:`596`
 
 
 Version 2.3.1
diff --git a/src/wtforms/meta.py b/src/wtforms/meta.py
index bea8df9a6..710ab58be 100644
--- a/src/wtforms/meta.py
+++ b/src/wtforms/meta.py
@@ -1,5 +1,6 @@
 from wtforms import i18n
 from wtforms.utils import WebobInputWrapper
+from wtforms.widgets.core import clean_key
 
 
 class DefaultMeta:
@@ -53,8 +54,12 @@ def render_field(self, field, render_kw):
 
         The default implementation calls ``field.widget(field, **render_kw)``
         """
+
+        render_kw = {clean_key(k): v for k, v in render_kw.items()}
+
         other_kw = getattr(field, "render_kw", None)
         if other_kw is not None:
+            other_kw = {clean_key(k): v for k, v in other_kw.items()}
             render_kw = dict(other_kw, **render_kw)
         return field.widget(field, **render_kw)
 
diff --git a/src/wtforms/widgets/core.py b/src/wtforms/widgets/core.py
index 5be3f4041..3e2a2ebef 100644
--- a/src/wtforms/widgets/core.py
+++ b/src/wtforms/widgets/core.py
@@ -17,6 +17,13 @@
 )
 
 
+def clean_key(key):
+    key = key.rstrip("_")
+    if key.startswith("data_") or key.startswith("aria_"):
+        key = key.replace("_", "-")
+    return key
+
+
 def html_params(**kwargs):
     """
     Generate HTML attribute syntax from inputted keyword arguments.
@@ -53,10 +60,7 @@ def html_params(**kwargs):
     """
     params = []
     for k, v in sorted(kwargs.items()):
-        if k in ("class_", "class__", "for_"):
-            k = k[:-1]
-        elif k.startswith("data_") or k.startswith("aria_"):
-            k = k.replace("_", "-")
+        k = clean_key(k)
         if v is True:
             params.append(k)
         elif v is False:
diff --git a/tests/test_fields.py b/tests/test_fields.py
index cde794501..186bcead6 100644
--- a/tests/test_fields.py
+++ b/tests/test_fields.py
@@ -233,6 +233,37 @@ def test_render_kw(self):
             'type="text" value="hello">'
         )
 
+    def test_render_special(self):
+        class F(Form):
+            s = StringField(render_kw={"class_": "foo"})
+
+        assert '<input class="foo" id="s" name="s" type="text" value="">' == F().s()
+        assert '<input class="bar" id="s" name="s" type="text" value="">' == F().s(
+            **{"class": "bar"}
+        )
+        assert '<input class="bar" id="s" name="s" type="text" value="">' == F().s(
+            **{"class_": "bar"}
+        )
+
+        class G(Form):
+            s = StringField(render_kw={"class__": "foo"})
+
+        assert '<input class="foo" id="s" name="s" type="text" value="">' == G().s()
+        assert '<input class="bar" id="s" name="s" type="text" value="">' == G().s(
+            **{"class__": "bar"}
+        )
+
+        class H(Form):
+            s = StringField(render_kw={"for_": "foo"})
+
+        assert '<input for="foo" id="s" name="s" type="text" value="">' == H().s()
+        assert '<input for="bar" id="s" name="s" type="text" value="">' == H().s(
+            **{"for": "bar"}
+        )
+        assert '<input for="bar" id="s" name="s" type="text" value="">' == H().s(
+            **{"for_": "bar"}
+        )
+
     def test_select_field_copies_choices(self):
         class F(Form):
             items = SelectField(choices=[])
diff --git a/tests/test_widgets.py b/tests/test_widgets.py
index 11d724c7b..3bcb70be9 100644
--- a/tests/test_widgets.py
+++ b/tests/test_widgets.py
@@ -20,9 +20,6 @@
 class TestHTMLParams:
     def test_basic(self):
         assert html_params(foo=9, k="wuuu") == 'foo="9" k="wuuu"'
-        assert html_params(class_="foo") == 'class="foo"'
-        assert html_params(class__="foo") == 'class_="foo"'
-        assert html_params(for_="foo") == 'for="foo"'
         assert html_params(readonly=False, foo=9) == 'foo="9"'
         assert (
             html_params(accept="image/png, image/jpeg", required=True)