diff --git a/auditlog/management/commands/auditlogmigratejson.py b/auditlog/management/commands/auditlogmigratejson.py
index 44871a8..86caf25 100644
--- a/auditlog/management/commands/auditlogmigratejson.py
+++ b/auditlog/management/commands/auditlogmigratejson.py
@@ -125,7 +125,13 @@ class Command(BaseCommand):
         def postgres():
             with connection.cursor() as cursor:
                 cursor.execute(
-                    'UPDATE auditlog_logentry SET changes="changes_text"::jsonb'
+                    """
+                    UPDATE auditlog_logentry
+                    SET changes="changes_text"::jsonb
+                    WHERE changes_text IS NOT NULL
+                        AND changes_text <> ''
+                        AND changes IS NULL
+                    """
                 )
                 return cursor.cursor.rowcount
 
diff --git a/auditlog_tests/test_two_step_json_migration.py b/auditlog_tests/test_two_step_json_migration.py
index 5beb560..0b3bfff 100644
--- a/auditlog_tests/test_two_step_json_migration.py
+++ b/auditlog_tests/test_two_step_json_migration.py
@@ -135,6 +135,21 @@ class AuditlogMigrateJsonTest(TestCase):
         self.assertEqual(errbuf, "")
         self.assertIsNotNone(log_entry.changes)
 
+    def test_native_postgres_changes_not_overwritten(self):
+        # Arrange
+        log_entry = self.make_logentry()
+        log_entry.changes = original_changes = {"key": "value"}
+        log_entry.changes_text = '{"key": "new value"}'
+        log_entry.save()
+
+        # Act
+        outbuf, errbuf = self.call_command("-d=postgres")
+        log_entry.refresh_from_db()
+
+        # Assert
+        self.assertEqual(errbuf, "")
+        self.assertEqual(log_entry.changes, original_changes)
+
     def test_native_unsupported(self):
         # Arrange
         log_entry = self.make_logentry()