diff --git a/backend/open_webui/tools/builtin.py b/backend/open_webui/tools/builtin.py
index dcbdfe5201..dd1c38fdd7 100644
--- a/backend/open_webui/tools/builtin.py
+++ b/backend/open_webui/tools/builtin.py
@@ -539,7 +539,9 @@ async def ask_user(
     :return: JSON with status and answers keyed by question id
     """
     try:
-        if not isinstance(questions, list) or not 1 <= len(questions) <= 3:
+        if not isinstance(questions, list):
+            raise ValueError('ask_user questions must be an array of question objects.')
+        if not 1 <= len(questions) <= 3:
             raise ValueError('ask_user requires 1-3 questions.')
 
         normalized_questions = []
diff --git a/backend/open_webui/utils/ask_user.py b/backend/open_webui/utils/ask_user.py
index 14f5da6ad0..94bc648ef2 100644
--- a/backend/open_webui/utils/ask_user.py
+++ b/backend/open_webui/utils/ask_user.py
@@ -24,7 +24,9 @@ def get_ask_user_tool_calls(tool_calls: list[dict]) -> tuple[list[dict], str | N
 
 def normalize_ask_user_request(arguments: dict) -> dict:
     questions = arguments.get('questions')
-    if not isinstance(questions, list) or not 1 <= len(questions) <= 3:
+    if not isinstance(questions, list):
+        raise ValueError('ask_user questions must be an array of question objects.')
+    if not 1 <= len(questions) <= 3:
         raise ValueError('ask_user requires 1-3 questions.')
 
     normalized_questions = []