diff --git a/src/fold.c b/src/fold.c
index 67d542c..e1dda7e 100644
--- a/src/fold.c
+++ b/src/fold.c
@@ -3188,7 +3188,7 @@
 		--flp->lvl_next;
 	}
 	else
-	    ++s;
+	    mb_ptr_adv(s);
     }
 
     /* The level can't go negative, must be missing a start marker. */