diff --git a/include/block/aio.h b/include/block/aio.h
index f38b584ac7..6049e6a0f4 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -746,6 +746,21 @@ void coroutine_fn aio_co_reschedule_self(AioContext *new_ctx);
  * aio_co_wake may be executed either in coroutine or non-coroutine
  * context.  The coroutine must not be entered by anyone else while
  * aio_co_wake() is active.
+ *
+ * If `co`'s AioContext differs from the current AioContext, this will call
+ * aio_co_schedule(), which makes this safe to use even when `co` has not
+ * yielded yet.  In such a case, it will be entered once it yields.
+ *
+ * In contrast, if `co`'s AioContext is equal to the current one, it is
+ * required for `co` to currently be yielding.  This is generally the case
+ * if the caller is not in `co` (i.e. invoked by `co`), because the only
+ * other way for the caller to be running then is for `co` to currently be
+ * yielding.
+ *
+ * Therefore, if there is no way for the caller to be invoked/entered by
+ * `co`, it is generally safe to call this regardless of whether `co` is
+ * known to already be yielding or not -- it only has to yield at some
+ * point.
  */
 void aio_co_wake(Coroutine *co);