diff --git a/rclpy/rclpy/__init__.py b/rclpy/rclpy/__init__.py
index c14184ec4..3c8a9b751 100644
--- a/rclpy/rclpy/__init__.py
+++ b/rclpy/rclpy/__init__.py
@@ -207,6 +207,9 @@ def spin_once(
     It is possible the work done is for a node other than the one provided if the global executor
     has a partially completed coroutine.
 
+    This method should not be called from multiple threads with the same node or executor
+    argument.
+
     :param node: A node to add to the executor to check for work.
     :param executor: The executor to use, or the global executor if ``None``.
     :param timeout_sec: Seconds to wait. Block forever if ``None`` or negative. Don't wait if 0.
diff --git a/rclpy/rclpy/executors.py b/rclpy/rclpy/executors.py
index 52b814b6d..a6ed8e508 100644
--- a/rclpy/rclpy/executors.py
+++ b/rclpy/rclpy/executors.py
@@ -339,6 +339,8 @@ def spin_once(self, timeout_sec: Optional[float] = None) -> None:
 
         A custom executor should use :meth:`wait_for_ready_callbacks` to get work.
 
+        This method should not be called from multiple threads.
+
         :param timeout_sec: Seconds to wait. Block forever if ``None`` or negative.
             Don't wait if 0.
         """