1 files changed, 3 insertions, 0 deletions

diff --git a/src/alloc.c b/src/alloc.c
index 20b8981bd66..be55dcf8dfd 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -6505,6 +6505,9 @@ mark_char_table (struct Lisp_Vector *ptr, enum pvec_type pvectype)
 static void
 mark_overlay (struct Lisp_Overlay *ov)
 {
+  /* We don't mark the `interval_node` object, because it is managed manually
+     rather than by the GC.  */
+  eassert (BASE_EQ (ov->interval->data, make_lisp_ptr (ov, Lisp_Vectorlike)));
   set_vectorlike_marked (&ov->header);
   mark_object (ov->plist);
 }