diff --git a/vllm/entrypoints/openai/responses/protocol.py b/vllm/entrypoints/openai/responses/protocol.py
index ff3331612f..48827ff941 100644
--- a/vllm/entrypoints/openai/responses/protocol.py
+++ b/vllm/entrypoints/openai/responses/protocol.py
@@ -622,8 +622,15 @@ class ResponsesRequest(OpenAIBaseModel):
                 if isinstance(tool, dict):
                     if tool.get("type") == "namespace":
                         namespace = tool.get("name")
-                        for namespaced_tool in tool.get("tools", []):
-                            namespaced_name = namespaced_tool.get("name")
+                        namespaced_tools = tool.get("tools")
+                        if not isinstance(namespaced_tools, list):
+                            return data
+                        for namespaced_tool in namespaced_tools:
+                            namespaced_name = (
+                                namespaced_tool.get("name")
+                                if isinstance(namespaced_tool, dict)
+                                else getattr(namespaced_tool, "name", None)
+                            )
                             tool_names.add(namespaced_name)
                             tool_names.add(f"{namespace}__{namespaced_name}")
                     else: