diff --git a/model_utils/tracker.py b/model_utils/tracker.py
index eab1d4af..1fa4a96f 100644
--- a/model_utils/tracker.py
+++ b/model_utils/tracker.py
@@ -332,12 +332,12 @@ def _get_field_name(self) -> str:
 
         self.instance._deferred_fields = self.instance.get_deferred_fields()
         for field in self.instance._deferred_fields:
-            field_obj = self.instance.__class__.__dict__.get(field)
+            field_obj: models.Field = self.instance.__class__.__dict__[field]
             if isinstance(field_obj, FileDescriptor):
                 file_descriptor_tracker = FileDescriptorTracker(field_obj.field)
                 setattr(self.instance.__class__, field, file_descriptor_tracker)
             else:
-                deferred_attribute_tracker = DeferredAttributeTracker(field)
+                deferred_attribute_tracker = DeferredAttributeTracker(field_obj)
                 setattr(self.instance.__class__, field, deferred_attribute_tracker)