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1 files changed, 2 insertions, 0 deletions

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 47bdc26a..5ae8ff48 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -191,6 +191,8 @@ class WritableField(Field):
         except KeyError:
             if self.default is not None and not self.root.partial:
                 native = self.default
+                # partial serializers shouldn't set the default field to avoid
+                # overriding the previously set value
             else:
                 if self.required:
                     raise ValidationError(self.error_messages['required'])