diff --git a/kern/include/alarm.h b/kern/include/alarm.h
index 7510d1c..7f63470 100644
--- a/kern/include/alarm.h
+++ b/kern/include/alarm.h
@@ -103,6 +103,9 @@
 /* Unset and reset may block if the alarm is not IRQ.  Do not call from within a
  * handler.  Returns TRUE if you stopped the alarm from firing. */
 bool unset_alarm(struct timer_chain *tchain, struct alarm_waiter *waiter);
+/* Will not block; handler may still be running. */
+bool unset_alarm_nosync(struct timer_chain *tchain,
+			struct alarm_waiter *waiter);
 /* Convenience wrappers for unset, then set.  Slower, but easier than just
  * setting, since you don't need to know if it fired.  Returns TRUE if the alarm
  * did not fire before your reset. */
diff --git a/kern/src/alarm.c b/kern/src/alarm.c
index 6ee32e8..3ff6534 100644
--- a/kern/src/alarm.c
+++ b/kern/src/alarm.c
@@ -277,12 +277,26 @@
 	}
 }
 
+bool unset_alarm_nosync(struct timer_chain *tchain, struct alarm_waiter *waiter)
+{
+	bool ret = false;
+
+	spin_lock_irqsave(&tchain->lock);
+	if (waiter->on_tchain) {
+		if (__remove_awaiter(tchain, waiter))
+			reset_tchain_interrupt(tchain);
+		ret = true;
+	}
+	spin_unlock_irqsave(&tchain->lock);
+	return ret;
+}
+
 bool reset_alarm_abs(struct timer_chain *tchain, struct alarm_waiter *waiter,
                      uint64_t abs_time)
 {
 	bool ret;
 
-	ret = unset_alarm(tchain, waiter);
+	ret = unset_alarm_nosync(tchain, waiter);
 	set_awaiter_abs(waiter, abs_time);
 	set_alarm(tchain, waiter);
 	return ret;
@@ -293,7 +307,7 @@
 {
 	bool ret;
 
-	ret = unset_alarm(tchain, waiter);
+	ret = unset_alarm_nosync(tchain, waiter);
 	set_awaiter_rel(waiter, usleep);
 	set_alarm(tchain, waiter);
 	return ret;