diff --git a/litellm/litellm_core_utils/prompt_templates/factory.py b/litellm/litellm_core_utils/prompt_templates/factory.py
index d3197972862..ad966fde244 100644
--- a/litellm/litellm_core_utils/prompt_templates/factory.py
+++ b/litellm/litellm_core_utils/prompt_templates/factory.py
@@ -1261,6 +1261,13 @@ def encode_tool_call_id_with_signature(tool_call_id: str, thought_signature: str
 _encode_tool_call_id_with_signature = encode_tool_call_id_with_signature
 
 
+def _same_tool_call(tool_call_id: str, other_tool_call_id: str) -> bool:
+    return (
+        tool_call_id.split(THOUGHT_SIGNATURE_SEPARATOR, 1)[0]
+        == other_tool_call_id.split(THOUGHT_SIGNATURE_SEPARATOR, 1)[0]
+    )
+
+
 def embeds_thought_signature_in_tool_call_id(litellm_params: Mapping[str, object]) -> bool:
     return litellm_params.get("thought_signature_in_tool_call_id") is not False
 
@@ -1609,7 +1616,13 @@ def convert_to_gemini_tool_call_result(
         msg_tool_call_id: Final = message.get("tool_call_id", None)
         for tool in tools:
             prev_tool_call_id = tool.get("id", None)
-            if msg_tool_call_id and prev_tool_call_id and msg_tool_call_id == prev_tool_call_id:
+            if (
+                isinstance(msg_tool_call_id, str)
+                and isinstance(prev_tool_call_id, str)
+                and msg_tool_call_id
+                and prev_tool_call_id
+                and _same_tool_call(msg_tool_call_id, prev_tool_call_id)
+            ):
                 name = tool.get("function", {}).get("name", "")
 
     # Echo the OpenAI tool_call_id on functionResponse (strip thought-signature suffix).
diff --git a/tests/unit/llms/vertex_ai/gemini/test_thought_signature_in_tool_call_id.py b/tests/unit/llms/vertex_ai/gemini/test_thought_signature_in_tool_call_id.py
index 1146e7dac0c..2df7d0b3dd3 100644
--- a/tests/unit/llms/vertex_ai/gemini/test_thought_signature_in_tool_call_id.py
+++ b/tests/unit/llms/vertex_ai/gemini/test_thought_signature_in_tool_call_id.py
@@ -430,3 +430,47 @@ def test_bounded_tool_call_id_round_trips_to_gemini(client_keeps_provider_fields
     assert len(replayed_signatures) == 1
     assert (replayed_signatures[0] == LONG_SIGNATURE) is client_keeps_provider_fields
     assert replayed_signatures[0]
+
+
+def test_tool_result_with_bare_id_matches_call_whose_id_the_client_re_signed():
+    bare_id: Final = "call_601401"
+    with respx.mock:
+        route: Final = respx.post(url__regex=GEMINI_URL_PATTERN).mock(
+            return_value=httpx.Response(
+                200,
+                json={
+                    "candidates": [
+                        {"content": {"role": "model", "parts": [{"text": "Sunny"}]}, "finishReason": "STOP", "index": 0}
+                    ],
+                    "usageMetadata": {"promptTokenCount": 9, "candidatesTokenCount": 1, "totalTokenCount": 10},
+                },
+            )
+        )
+        litellm.completion(
+            model="gemini/gemini-3.5-flash",
+            messages=[
+                USER_TURN,
+                {
+                    "role": "assistant",
+                    "content": None,
+                    "tool_calls": [
+                        {
+                            "id": encode_tool_call_id_with_signature(bare_id, LONG_SIGNATURE),
+                            "type": "function",
+                            "function": {"name": "get_weather", "arguments": '{"city": "Paris"}'},
+                        }
+                    ],
+                },
+                {"role": "tool", "tool_call_id": bare_id, "content": '{"temp_c": 21}'},
+            ],
+            tools=[WEATHER_TOOL],
+            api_key="test-gemini-key",
+            thought_signature_in_tool_call_id=False,
+        )
+        sent_body: Final = json.loads(route.calls.last.request.content)
+
+    parts: Final = list(chain.from_iterable(turn["parts"] for turn in sent_body["contents"]))
+    function_calls: Final = [part for part in parts if "function_call" in part]
+    function_responses: Final = [part["function_response"] for part in parts if "function_response" in part]
+    assert [part["thoughtSignature"] for part in function_calls] == [LONG_SIGNATURE]
+    assert [response["name"] for response in function_responses] == ["get_weather"]
diff --git a/tests/unit/proxy/pass_through_endpoints/llm_provider_handlers/test_gemini_passthrough_logging_handler.py b/tests/unit/proxy/pass_through_endpoints/llm_provider_handlers/test_gemini_passthrough_logging_handler.py
index f780c056f64..31d95984996 100644
--- a/tests/unit/proxy/pass_through_endpoints/llm_provider_handlers/test_gemini_passthrough_logging_handler.py
+++ b/tests/unit/proxy/pass_through_endpoints/llm_provider_handlers/test_gemini_passthrough_logging_handler.py
@@ -83,6 +83,7 @@ class TestGeminiPassthroughLoggingHandler:
         mock_logging_obj = MagicMock(spec=LiteLLMLoggingObj)
         mock_logging_obj.model_call_details = {}
         mock_logging_obj.optional_params = {}
+        mock_logging_obj.litellm_params = {}
         mock_logging_obj.litellm_call_id = "test-call-id-123"
         return mock_logging_obj
 
diff --git a/tests/unit/proxy/pass_through_endpoints/test_streaming_handler.py b/tests/unit/proxy/pass_through_endpoints/test_streaming_handler.py
index da084146894..8bae17ed8b7 100644
--- a/tests/unit/proxy/pass_through_endpoints/test_streaming_handler.py
+++ b/tests/unit/proxy/pass_through_endpoints/test_streaming_handler.py
@@ -83,6 +83,7 @@ def _logging_obj() -> LiteLLMLoggingObj:
     logging_obj = MagicMock(spec=LiteLLMLoggingObj)
     logging_obj.model_call_details = {}
     logging_obj.optional_params = {}
+    logging_obj.litellm_params = {}
     logging_obj.litellm_call_id = "test-call-id"
     return logging_obj
 
diff --git a/tests/unit/types/test_litellm_params.py b/tests/unit/types/test_litellm_params.py
index 788d405f99f..d2aed5853ae 100644
--- a/tests/unit/types/test_litellm_params.py
+++ b/tests/unit/types/test_litellm_params.py
@@ -217,6 +217,7 @@ OPTION_NAMES: Final = (
     "assistant_continue_message",
     "disable_add_transform_inline_image_block",
     "merge_reasoning_content_in_choices",
+    "thought_signature_in_tool_call_id",
     "enable_json_schema_validation",
     "complete_response",
     "stream_chunk_size",