diff --git a/litellm/llms/bedrock_mantle/responses/transformation.py b/litellm/llms/bedrock_mantle/responses/transformation.py
index b35418edd6d..e1b12d03a11 100644
--- a/litellm/llms/bedrock_mantle/responses/transformation.py
+++ b/litellm/llms/bedrock_mantle/responses/transformation.py
@@ -16,7 +16,7 @@ BaseAWSLLM._sign_request after the request body is finalized.
 import re
 from typing import Optional, Tuple
 
-from botocore.exceptions import NoCredentialsError
+from botocore.exceptions import BotoCoreError
 
 from litellm.llms.bedrock.base_aws_llm import BaseAWSLLM
 from litellm.llms.openai.responses.transformation import OpenAIResponsesAPIConfig
@@ -152,7 +152,7 @@ class BedrockMantleResponsesAPIConfig(OpenAIResponsesAPIConfig):
                 stream=stream,
                 fake_stream=fake_stream,
             )
-        except NoCredentialsError as e:
+        except BotoCoreError as e:
             raise ValueError(
                 "Bedrock Mantle auth failed: no Bearer token and no usable AWS "
                 "credentials. Set BEDROCK_MANTLE_API_KEY (or AWS_BEARER_TOKEN_BEDROCK) "
diff --git a/tests/test_litellm/llms/bedrock_mantle/test_bedrock_mantle_responses_transformation.py b/tests/test_litellm/llms/bedrock_mantle/test_bedrock_mantle_responses_transformation.py
index cdeb249196f..7771049913a 100644
--- a/tests/test_litellm/llms/bedrock_mantle/test_bedrock_mantle_responses_transformation.py
+++ b/tests/test_litellm/llms/bedrock_mantle/test_bedrock_mantle_responses_transformation.py
@@ -12,6 +12,7 @@ import sys
 sys.path.insert(0, os.path.abspath("../../../../.."))
 
 import pytest
+from botocore.exceptions import PartialCredentialsError, ProfileNotFound
 
 import litellm
 from litellm.llms.bedrock_mantle.responses.transformation import (
@@ -578,6 +579,36 @@ class TestBedrockMantleResponsesSigV4:
         assert "Bearer" in msg
         assert "SigV4" in msg or "IAM" in msg
 
+    @pytest.mark.parametrize(
+        "cred_error",
+        [
+            PartialCredentialsError(provider="env", cred_var="aws_secret_access_key"),
+            ProfileNotFound(profile="missing-profile"),
+        ],
+    )
+    def test_partial_credentials_raises_both_paths(self, monkeypatch, cred_error):
+        from unittest.mock import MagicMock
+        from litellm.llms.bedrock.base_aws_llm import BaseAWSLLM
+
+        monkeypatch.delenv("BEDROCK_MANTLE_API_KEY", raising=False)
+        monkeypatch.delenv("AWS_BEARER_TOKEN_BEDROCK", raising=False)
+
+        signer = BaseAWSLLM()
+        signer.get_credentials = MagicMock(side_effect=cred_error)
+        cfg = BedrockMantleResponsesAPIConfig(aws_signer=signer)
+
+        with pytest.raises(ValueError) as exc:
+            cfg.sign_request(
+                headers={},
+                optional_params={"aws_region_name": "us-east-2"},
+                request_data={"input": "hi"},
+                api_base="https://bedrock-mantle.us-east-2.api.aws/openai/v1/responses",
+                api_key=None,
+            )
+        msg = str(exc.value)
+        assert "Bearer" in msg
+        assert "SigV4" in msg or "IAM" in msg
+
 
 class TestBedrockMantleResponsesPricing:
     def test_gpt_5_5_pricing_and_mode(self, local_cost_map):