diff --git a/auditlog/diff.py b/auditlog/diff.py
index bd5fe59..c246c8a 100644
--- a/auditlog/diff.py
+++ b/auditlog/diff.py
@@ -206,11 +206,13 @@ def model_instance_diff(
 
         if old_value != new_value:
             if field.name in custom_fields_callbacks:
-                new_value = custom_fields_callbacks[field.name](
+                deepdiff_result = custom_fields_callbacks[field.name](
                     json.dumps(old_value), json.dumps(new_value)
                 )
-                old_value = " FIELD TOO LARGE "
-                diff[field.name] = (smart_str(old_value), smart_str(new_value))
+                diff[field.name] = (
+                    "[CUSTOM FIELD] Showing only the differences ->",
+                    deepdiff_result,
+                )
             elif model_fields and field.name in model_fields["mask_fields"]:
                 diff[field.name] = (
                     mask_str(smart_str(old_value)),