diff --git a/litellm/proxy/guardrails/anthropic_sse.py b/litellm/proxy/guardrails/anthropic_sse.py
index 43a812cb4b5..3c7580a14a4 100644
--- a/litellm/proxy/guardrails/anthropic_sse.py
+++ b/litellm/proxy/guardrails/anthropic_sse.py
@@ -92,16 +92,17 @@ def model_response_text(response: ModelResponse) -> str:
     )
 
 
-def anthropic_sse_error_frames(message: str) -> tuple[bytes, ...]:
+def anthropic_sse_error_frames(message: str | Mapping[str, object]) -> tuple[bytes, ...]:
     """Anthropic error event, for a failure discovered after the response headers were flushed.
 
     Once a keepalive ping has been sent a raise cannot reach the client, so the failure has to
-    travel as a frame.
+    travel as a frame. A structured message is emitted as JSON rather than stringified, so the
+    guardrail's own detail stays machine readable.
     """
-    detail: Final = json.dumps(message)
+    body: Final = json.dumps(message, default=str)
     return (
         f'event: error\ndata: {{"type": "error", "error": {{"type": "guardrail_error", '
-        f'"message": {detail}}}}}\n\n'.encode(),
+        f'"message": {body}}}}}\n\n'.encode(),
     )
 
 
diff --git a/litellm/proxy/guardrails/guardrail_hooks/bedrock_guardrails.py b/litellm/proxy/guardrails/guardrail_hooks/bedrock_guardrails.py
index a6852b6fb0b..d3c3a61201b 100644
--- a/litellm/proxy/guardrails/guardrail_hooks/bedrock_guardrails.py
+++ b/litellm/proxy/guardrails/guardrail_hooks/bedrock_guardrails.py
@@ -2625,7 +2625,10 @@ class BedrockGuardrail(CustomGuardrail, BaseAWSLLM):
                     raise
                 # A keepalive ping may already have flushed the response headers, so a raise
                 # cannot reach the client; deliver the block as an error frame instead
-                for error_frame in anthropic_sse_error_frames(str(block_exc.detail)):
+                block_detail: Final = block_exc.detail
+                for error_frame in anthropic_sse_error_frames(
+                    block_detail if isinstance(block_detail, Mapping) else str(block_detail)
+                ):
                     yield error_frame
                 return
             except ModifyResponseException as e: