diff --git a/mongoengine/queryset/transform.py b/mongoengine/queryset/transform.py
index 057218508..cb2a4a66c 100644
--- a/mongoengine/queryset/transform.py
+++ b/mongoengine/queryset/transform.py
@@ -1,3 +1,5 @@
+import re
+
 from collections import defaultdict
 
 from bson import ObjectId, SON
@@ -147,7 +149,7 @@ def query(_doc_cls=None, **kwargs):
         if op is None or key not in mongo_query:
             mongo_query[key] = value
         elif key in mongo_query:
-            if isinstance(mongo_query[key], dict):
+            if isinstance(mongo_query[key], dict) and not isinstance(value, re._pattern_type):
                 mongo_query[key].update(value)
                 # $max/minDistance needs to come last - convert to SON
                 value_dict = mongo_query[key]
diff --git a/tests/queryset/transform.py b/tests/queryset/transform.py
index a043a6472..01fd2758f 100644
--- a/tests/queryset/transform.py
+++ b/tests/queryset/transform.py
@@ -248,6 +248,12 @@ class Event(Document):
         with self.assertRaises(InvalidQueryError):
             events.count()
 
+    def test_and_filtering_with_same_key_and_regex(self):
+        class Doc(Document):
+            value = StringField()
+
+        Doc.objects.filter(Q(value__startswith="test")&Q(value__not__startswith="test2")).count()
+
 
 if __name__ == '__main__':
     unittest.main()