diff --git a/js/plugins/googleai/src/gemini.ts b/js/plugins/googleai/src/gemini.ts
index 38d8285856..6e96412ffe 100644
--- a/js/plugins/googleai/src/gemini.ts
+++ b/js/plugins/googleai/src/gemini.ts
@@ -1016,7 +1016,7 @@ function fromGeminiPart(
   jsonMode: boolean,
   ref: string
 ): Part {
-  if ('thought' in part) return fromThought(part as any);
+  if ('thought' in part || 'thoughtSignature' in part) return fromThought(part as any);
   if (typeof part.text === 'string') return { text: part.text };
   if (part.inlineData) return fromInlineData(part);
   if (part.functionCall) return fromFunctionCall(part, ref);
diff --git a/js/plugins/vertexai/src/gemini.ts b/js/plugins/vertexai/src/gemini.ts
index 9509099a03..6ebafd7076 100644
--- a/js/plugins/vertexai/src/gemini.ts
+++ b/js/plugins/vertexai/src/gemini.ts
@@ -888,7 +888,7 @@ function fromGeminiPart(
   jsonMode: boolean,
   ref?: string
 ): Part {
-  if ('thought' in part) return fromGeminiThought(part as any);
+  if ('thought' in part || 'thoughtSignature' in part) return fromGeminiThought(part as any);
   if (typeof part.text === 'string') return { text: part.text };
   if (part.inlineData) return fromGeminiInlineDataPart(part);
   if (part.fileData) return fromGeminiFileDataPart(part);