diff --git a/metagpt/tools/search_engine_serpapi.py b/metagpt/tools/search_engine_serpapi.py
index 4fd2b94b8..9d2d20af6 100644
--- a/metagpt/tools/search_engine_serpapi.py
+++ b/metagpt/tools/search_engine_serpapi.py
@@ -18,7 +18,7 @@ class SerpAPIWrapper(BaseModel):
 
     search_engine: Any = None  #: :meta private:
     params: dict = Field(
-        default={
+        default_factory=lambda: {
             "engine": "google",
             "google_domain": "google.com",
             "gl": "us",
diff --git a/metagpt/tools/search_engine_serper.py b/metagpt/tools/search_engine_serper.py
index 3707d905d..3dc1d3591 100644
--- a/metagpt/tools/search_engine_serper.py
+++ b/metagpt/tools/search_engine_serper.py
@@ -9,14 +9,16 @@ import json
 from typing import Any, Dict, Optional, Tuple
 
 import aiohttp
-from pydantic import BaseModel, Field, field_validator
+from pydantic import BaseModel, ConfigDict, Field, field_validator
 
 from metagpt.config import CONFIG
 
 
 class SerperWrapper(BaseModel):
+    model_config = ConfigDict(arbitrary_types_allowed=True)
+
     search_engine: Any = None  #: :meta private:
-    payload: dict = Field(default={"page": 1, "num": 10})
+    payload: dict = Field(default_factory=lambda: {"page": 1, "num": 10})
     serper_api_key: Optional[str] = Field(default=None, validate_default=True)
     aiosession: Optional[aiohttp.ClientSession] = None
 
diff --git a/tests/metagpt/tools/test_search_engine.py b/tests/metagpt/tools/test_search_engine.py
index 47b50337f..dcf1eec69 100644
--- a/tests/metagpt/tools/test_search_engine.py
+++ b/tests/metagpt/tools/test_search_engine.py
@@ -58,7 +58,7 @@ async def test_search_engine(search_engine_type, run_func: Callable, max_results
         assert isinstance(rsp, str)
     else:
         assert isinstance(rsp, list)
-        assert len(rsp) == max_results
+        assert len(rsp) <= max_results
 
 
 if __name__ == "__main__":