diff --git a/src/smolagents/default_tools.py b/src/smolagents/default_tools.py
index d3cf1e6..d290e6f 100644
--- a/src/smolagents/default_tools.py
+++ b/src/smolagents/default_tools.py
@@ -257,17 +257,15 @@ class SpeechToTextTool(PipelineTool):
     }
     output_type = "string"
 
-    def __new__(cls):
+    def __new__(cls, *args, **kwargs):
         from transformers.models.whisper import (
             WhisperForConditionalGeneration,
             WhisperProcessor,
         )
 
-        if not hasattr(cls, "pre_processor_class"):
-            cls.pre_processor_class = WhisperProcessor
-        if not hasattr(cls, "model_class"):
-            cls.model_class = WhisperForConditionalGeneration
-        return super().__new__()
+        cls.pre_processor_class = WhisperProcessor
+        cls.model_class = WhisperForConditionalGeneration
+        return super().__new__(cls, *args, **kwargs)
 
     def encode(self, audio):
         audio = AgentAudio(audio).to_raw()
diff --git a/tests/test_default_tools.py b/tests/test_default_tools.py
index e3cb4a6..5ff436e 100644
--- a/tests/test_default_tools.py
+++ b/tests/test_default_tools.py
@@ -17,7 +17,7 @@ import unittest
 import pytest
 
 from smolagents.agent_types import _AGENT_TYPE_MAPPING
-from smolagents.default_tools import DuckDuckGoSearchTool, PythonInterpreterTool, VisitWebpageTool
+from smolagents.default_tools import DuckDuckGoSearchTool, PythonInterpreterTool, SpeechToTextTool, VisitWebpageTool
 
 from .test_tools import ToolTesterMixin
 
@@ -77,3 +77,13 @@ class PythonInterpreterToolTester(unittest.TestCase, ToolTesterMixin):
         with pytest.raises(Exception) as e:
             self.tool("import sympy as sp")
         assert "sympy" in str(e).lower()
+
+
+class TestSpeechToTextTool:
+    def test_new_instance(self):
+        from transformers.models.whisper import WhisperForConditionalGeneration, WhisperProcessor
+
+        tool = SpeechToTextTool()
+        assert tool is not None
+        assert tool.pre_processor_class == WhisperProcessor
+        assert tool.model_class == WhisperForConditionalGeneration