diff --git a/drivers/isdn/hisax/hfc_pci.c b/drivers/isdn/hisax/hfc_pci.c
index 8e5b03161b2ff..64a63711fd953 100644
--- a/drivers/isdn/hisax/hfc_pci.c
+++ b/drivers/isdn/hisax/hfc_pci.c
@@ -1170,11 +1170,13 @@ HFCPCI_l1hw(struct PStack *st, int pr, void *arg)
 		if (cs->debug & L1_DEB_LAPD)
 			debugl1(cs, "-> PH_REQUEST_PULL");
 #endif
+		spin_lock_irqsave(&cs->lock, flags);
 		if (!cs->tx_skb) {
 			test_and_clear_bit(FLG_L1_PULL_REQ, &st->l1.Flags);
 			st->l1.l1l2(st, PH_PULL | CONFIRM, NULL);
 		} else
 			test_and_set_bit(FLG_L1_PULL_REQ, &st->l1.Flags);
+		spin_unlock_irqrestore(&cs->lock, flags);
 		break;
 	case (HW_RESET | REQUEST):
 		spin_lock_irqsave(&cs->lock, flags);