diff --git a/django/forms/fields.py b/django/forms/fields.py
index 00e9ff102b..2facb74b1d 100644
--- a/django/forms/fields.py
+++ b/django/forms/fields.py
@@ -488,7 +488,7 @@ class DurationField(Field):
             return None
         if isinstance(value, datetime.timedelta):
             return value
-        value = parse_duration(force_str(value))
+        value = parse_duration(force_text(value))
         if value is None:
             raise ValidationError(self.error_messages['invalid'], code='invalid')
         return value