diff --git a/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go b/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go
index 4d7bf686..573b8d45 100644
--- a/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go
+++ b/internal/translator/antigravity/openai/chat-completions/antigravity_openai_request.go
@@ -266,7 +266,11 @@ func ConvertOpenAIRequestToAntigravity(modelName string, inputRawJSON []byte, _
 						fargs := tc.Get("function.arguments").String()
 						node, _ = sjson.SetBytes(node, "parts."+itoa(p)+".functionCall.id", fid)
 						node, _ = sjson.SetBytes(node, "parts."+itoa(p)+".functionCall.name", fname)
-						node, _ = sjson.SetRawBytes(node, "parts."+itoa(p)+".functionCall.args", []byte(fargs))
+						if gjson.Valid(fargs) {
+							node, _ = sjson.SetRawBytes(node, "parts."+itoa(p)+".functionCall.args", []byte(fargs))
+						} else {
+							node, _ = sjson.SetBytes(node, "parts."+itoa(p)+".functionCall.args.params", []byte(fargs))
+						}
 						node, _ = sjson.SetBytes(node, "parts."+itoa(p)+".thoughtSignature", geminiCLIFunctionThoughtSignature)
 						p++
 						if fid != "" {