1 files changed, 3 insertions, 1 deletions

diff --git a/src/alloc.c b/src/alloc.c
index 6cbd63f716c..67ff3459e71 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -1533,7 +1533,9 @@ make_interval (void)
 static void
 mark_interval (register INTERVAL i, Lisp_Object dummy)
 {
-  eassert (!i->gcmarkbit);              /* Intervals are never shared.  */
+  /* Intervals should never be shared.  So, if extra internal checking is
+     enabled, GC aborts if it seems to have visited an interval twice.  */
+  eassert (!i->gcmarkbit);
   i->gcmarkbit = 1;
   mark_object (i->plist);
 }