Fixed #36913 -- Optimized MultipleChoiceField.validate().

1 files changed, 2 insertions, 1 deletions

diff --git a/django/forms/fields.py b/django/forms/fields.py
index 6408be2f06..7f978aa03d 100644
--- a/django/forms/fields.py
+++ b/django/forms/fields.py
@@ -965,7 +965,8 @@ class MultipleChoiceField(ChoiceField):
         if self.required and not value:
             raise ValidationError(self.error_messages["required"], code="required")
         # Validate that each value in the value list is in self.choices.
-        for val in value:
+        # Use set() to avoid redundant validation.
+        for val in set(value):
             if not self.valid_value(val):
                 raise ValidationError(
                     self.error_messages["invalid_choice"],