diff --git a/src/google/adk/models/anthropic_llm.py b/src/google/adk/models/anthropic_llm.py
index 9799209695..9811733fea 100644
--- a/src/google/adk/models/anthropic_llm.py
+++ b/src/google/adk/models/anthropic_llm.py
@@ -218,18 +218,15 @@ def _update_type_string(value_dict: dict[str, Any]):
   if "type" in value_dict:
     value_dict["type"] = value_dict["type"].lower()
 
+  if "properties" in value_dict:
+    for _, value in value_dict["properties"].items():
+      _update_type_string(value)
+
   if "items" in value_dict:
     # 'type' field could exist for items as well, this would be the case if
     # items represent primitive types.
     _update_type_string(value_dict["items"])
 
-    if "properties" in value_dict["items"]:
-      # There could be properties as well on the items, especially if the items
-      # are complex object themselves. We recursively traverse each individual
-      # property as well and fix the "type" value.
-      for _, value in value_dict["items"]["properties"].items():
-        _update_type_string(value)
-
 
 def function_declaration_to_tool_param(
     function_declaration: types.FunctionDeclaration,
diff --git a/tests/unittests/models/test_anthropic_llm.py b/tests/unittests/models/test_anthropic_llm.py
index fac5f46204..b0a282d170 100644
--- a/tests/unittests/models/test_anthropic_llm.py
+++ b/tests/unittests/models/test_anthropic_llm.py
@@ -275,6 +275,69 @@ def test_supported_models():
             },
         ),
     ),
+    (
+        "function_with_nested_object_parameter",
+        types.FunctionDeclaration(
+            name="update_profile",
+            description="Updates a user profile.",
+            parameters=types.Schema(
+                type=types.Type.OBJECT,
+                properties={
+                    "profile": types.Schema(
+                        type=types.Type.OBJECT,
+                        description="The profile data",
+                        properties={
+                            "name": types.Schema(
+                                type=types.Type.STRING,
+                                description="Full name",
+                            ),
+                            "address": types.Schema(
+                                type=types.Type.OBJECT,
+                                description="Mailing address",
+                                properties={
+                                    "city": types.Schema(
+                                        type=types.Type.STRING,
+                                    ),
+                                    "state": types.Schema(
+                                        type=types.Type.STRING,
+                                    ),
+                                },
+                            ),
+                        },
+                    ),
+                },
+                required=["profile"],
+            ),
+        ),
+        anthropic_types.ToolParam(
+            name="update_profile",
+            description="Updates a user profile.",
+            input_schema={
+                "type": "object",
+                "properties": {
+                    "profile": {
+                        "type": "object",
+                        "description": "The profile data",
+                        "properties": {
+                            "name": {
+                                "type": "string",
+                                "description": "Full name",
+                            },
+                            "address": {
+                                "type": "object",
+                                "description": "Mailing address",
+                                "properties": {
+                                    "city": {"type": "string"},
+                                    "state": {"type": "string"},
+                                },
+                            },
+                        },
+                    },
+                },
+                "required": ["profile"],
+            },
+        ),
+    ),
     (
         "function_with_parameters_json_schema",
         types.FunctionDeclaration(