diff --git a/lua/avante/providers/openai.lua b/lua/avante/providers/openai.lua
index ebb8402..05eb649 100644
--- a/lua/avante/providers/openai.lua
+++ b/lua/avante/providers/openai.lua
@@ -459,6 +459,7 @@ function M:parse_response(ctx, data_stream, _, opts)
         self:add_tool_use_message(ctx, tool_use, "generating", opts)
       else
         local tool_use = ctx.tool_use_list[tool_call.index + 1]
+        if tool_call["function"].arguments == vim.NIL then tool_call["function"].arguments = "" end
         tool_use.input_json = tool_use.input_json .. tool_call["function"].arguments
         -- self:add_tool_use_message(ctx, tool_use, "generating", opts)
       end