1 files changed, 4 insertions, 1 deletions

diff --git a/src/xterm.h b/src/xterm.h
index e0f59440734..22ffb63607c 100644
--- a/src/xterm.h
+++ b/src/xterm.h
@@ -703,7 +703,10 @@ struct scroll_bar {
    by this structure.  */
 
 /* For an event of kind selection_request_event,
-   this structure really describes the contents.  */
+   this structure really describes the contents.
+   **Don't make this struct longer!**
+   If it overlaps the frame_or_window field of struct input_event,
+   that will cause GC to crash.  */
 struct selection_input_event
 {
   int kind;