diff --git a/backend/open_webui/utils/middleware.py b/backend/open_webui/utils/middleware.py
index c90c52340b..5fb296fa58 100644
--- a/backend/open_webui/utils/middleware.py
+++ b/backend/open_webui/utils/middleware.py
@@ -375,9 +375,14 @@ def serialize_output(output: list) -> str:
             result_item = tool_outputs.get(call_id)
             if result_item:
                 result_text = ""
-                for out in result_item.get("output", []):
-                    if "text" in out:
-                        result_text += out.get("text", "")
+                for output in result_item.get("output", []):
+                    if "text" in output:
+                        output_text = output.get("text", "")
+                        result_text += (
+                            str(output_text)
+                            if not isinstance(output_text, str)
+                            else output_text
+                        )
                 files = result_item.get("files")
                 embeds = result_item.get("embeds", "")