diff --git a/src/core/marsh.c b/src/core/marsh.c
index 57370a4d..787be7d8 100644
--- a/src/core/marsh.c
+++ b/src/core/marsh.c
@@ -413,7 +413,6 @@ static void marshal_one_abstract(MarshalState *st, Janet x, int flags) {
         janet_abstract_incref(abstract);
         pushbyte(st, LB_THREADED_ABSTRACT);
         pushbytes(st, (uint8_t *) &abstract, sizeof(abstract));
-        MARK_SEEN();
         return;
     }
 #endif