diff --git a/packages/frontend/core/src/components/blocksuite/block-suite-editor/ai/provider.tsx b/packages/frontend/core/src/components/blocksuite/block-suite-editor/ai/provider.tsx
index 22f32bffc1..c02db9f392 100644
--- a/packages/frontend/core/src/components/blocksuite/block-suite-editor/ai/provider.tsx
+++ b/packages/frontend/core/src/components/blocksuite/block-suite-editor/ai/provider.tsx
@@ -82,7 +82,7 @@ export function setupAIProvider() {
     return textToText({
       ...options,
       params: {
-        tone: options.tone,
+        tone: options.tone.toLowerCase(),
       },
       content: options.input,
       promptName: 'Change tone to',