diff --git a/src/vim9execute.c b/src/vim9execute.c
index 6a6ec41..1a8058a 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -2068,7 +2068,7 @@
 }
 
 /*
- * Store a value in a list, dict or blob variable.
+ * Store a value in a list, dict, blob or object variable.
  * Returns OK, FAIL or NOTDONE (uncatchable error).
  */
     static int
@@ -2177,9 +2177,9 @@
 	{
 	    long	    lidx = (long)tv_idx->vval.v_number;
 	    blob_T	    *blob = tv_dest->vval.v_blob;
-	    varnumber_T nr;
-	    int	    error = FALSE;
-	    int	    len;
+	    varnumber_T	    nr;
+	    int		    error = FALSE;
+	    int		    len;
 
 	    if (blob == NULL)
 	    {
@@ -2209,6 +2209,7 @@
 	    long	    idx = (long)tv_idx->vval.v_number;
 	    object_T	    *obj = tv_dest->vval.v_object;
 	    typval_T	    *otv = (typval_T *)(obj + 1);
+	    clear_tv(&otv[idx]);
 	    otv[idx] = *tv;
 	}
 	else
@@ -4293,10 +4294,12 @@
 	    // Jump if an argument with a default value was already set and not
 	    // v:none.
 	    case ISN_JUMP_IF_ARG_SET:
+	    case ISN_JUMP_IF_ARG_NOT_SET:
 		tv = STACK_TV_VAR(iptr->isn_arg.jumparg.jump_arg_off);
-		if (tv->v_type != VAR_UNKNOWN
-			&& !(tv->v_type == VAR_SPECIAL
-					    && tv->vval.v_number == VVAL_NONE))
+		int arg_set = tv->v_type != VAR_UNKNOWN
+				&& !(tv->v_type == VAR_SPECIAL
+					    && tv->vval.v_number == VVAL_NONE);
+		if (iptr->isn_type == ISN_JUMP_IF_ARG_SET ? arg_set : !arg_set)
 		    ectx->ec_iidx = iptr->isn_arg.jumparg.jump_where;
 		break;
 
@@ -6633,6 +6636,12 @@
 						iptr->isn_arg.jump.jump_where);
 		break;
 
+	    case ISN_JUMP_IF_ARG_NOT_SET:
+		smsg("%s%4d JUMP_IF_ARG_NOT_SET arg[%d] -> %d", pfx, current,
+			 iptr->isn_arg.jumparg.jump_arg_off + STACK_FRAME_SIZE,
+						iptr->isn_arg.jump.jump_where);
+		break;
+
 	    case ISN_FOR:
 		{
 		    forloop_T *forloop = &iptr->isn_arg.forloop;