diff --git a/src/google/adk/tools/set_model_response_tool.py b/src/google/adk/tools/set_model_response_tool.py
index d1dc6ed55d..22605ad037 100644
--- a/src/google/adk/tools/set_model_response_tool.py
+++ b/src/google/adk/tools/set_model_response_tool.py
@@ -87,8 +87,17 @@ def set_model_response() -> str:
               annotation=list[inner_type],
           )
       ]
+    elif isinstance(output_schema, dict):
+      # Use `dict` type, not the instance — dict instances are unhashable.
+      params = [
+          inspect.Parameter(
+              'response',
+              inspect.Parameter.KEYWORD_ONLY,
+              annotation=dict,
+          )
+      ]
     else:
-      # For other schema types (list[str], dict, etc.),
+      # For other schema types (list[str], Schema, GenericAlias, etc.),
       # create a single parameter with the actual schema type
       params = [
           inspect.Parameter(
diff --git a/tests/unittests/tools/test_set_model_response_tool.py b/tests/unittests/tools/test_set_model_response_tool.py
index 89da394acc..6f2638a588 100644
--- a/tests/unittests/tools/test_set_model_response_tool.py
+++ b/tests/unittests/tools/test_set_model_response_tool.py
@@ -467,3 +467,18 @@ async def test_run_async_dict_schema():
   assert result is not None
   assert isinstance(result, dict)
   assert result == {'a': 1, 'b': 2, 'c': 3}
+
+
+def test_tool_initialization_raw_dict_instance():
+  """Test tool initialization with a raw dict schema instance."""
+  raw_schema = {'type': 'object', 'properties': {'name': {'type': 'string'}}}
+  tool = SetModelResponseTool(raw_schema)
+
+  assert tool.output_schema == raw_schema
+  assert not tool._is_basemodel
+  assert not tool._is_list_of_basemodel
+
+  sig = inspect.signature(tool.func)
+  assert 'response' in sig.parameters
+  assert len(sig.parameters) == 1
+  assert sig.parameters['response'].annotation is dict