diff --git a/service/error.go b/service/error.go
index cf7325b6..9d035858 100644
--- a/service/error.go
+++ b/service/error.go
@@ -123,7 +123,13 @@ func RelayErrorHandler(ctx context.Context, resp *http.Response, showBodyWhenFai
 			return
 		}
 	}
-	newApiErr = types.NewOpenAIError(errors.New(errResponse.ToMessage()), types.ErrorCodeBadResponseStatusCode, resp.StatusCode)
+	message := errResponse.ToMessage()
+	if message == "" {
+		// The body parsed as JSON but carried no usable error message; log the
+		// raw body so the upstream failure remains diagnosable.
+		logger.LogError(ctx, fmt.Sprintf("bad response status code %d with empty error message, body: %s", resp.StatusCode, responseBodyPreview))
+	}
+	newApiErr = types.NewOpenAIError(errors.New(message), types.ErrorCodeBadResponseStatusCode, resp.StatusCode)
 	if showBodyWhenFail {
 		newApiErr.Err = buildErrWithBody(newApiErr.Error())
 	}