diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c
index 8dafc3f2add42004a41ca68341ed619268909255..a853d8a29476d75e42f538057e4bc91a80e334cc 100644
--- a/arch/um/kernel/time.c
+++ b/arch/um/kernel/time.c
@@ -374,9 +374,29 @@ static void time_travel_update_time(unsigned long long next, bool idle)
 	time_travel_del_event(&ne);
 }
 
+static void time_travel_update_time_rel(unsigned long long offs)
+{
+	unsigned long flags;
+
+	/*
+	 * Disable interrupts before calculating the new time so
+	 * that a real timer interrupt (signal) can't happen at
+	 * a bad time e.g. after we read time_travel_time but
+	 * before we've completed updating the time.
+	 */
+	local_irq_save(flags);
+	time_travel_update_time(time_travel_time + offs, false);
+	local_irq_restore(flags);
+}
+
 void time_travel_ndelay(unsigned long nsec)
 {
-	time_travel_update_time(time_travel_time + nsec, false);
+	/*
+	 * Not strictly needed to use _rel() version since this is
+	 * only used in INFCPU/EXT modes, but it doesn't hurt and
+	 * is more readable too.
+	 */
+	time_travel_update_time_rel(nsec);
 }
 EXPORT_SYMBOL(time_travel_ndelay);
 
@@ -479,7 +499,11 @@ static int time_travel_connect_external(const char *socket)
 #define time_travel_start 0
 #define time_travel_time 0
 
-static inline void time_travel_update_time(unsigned long long ns, bool retearly)
+static inline void time_travel_update_time(unsigned long long ns, bool idle)
+{
+}
+
+static inline void time_travel_update_time_rel(unsigned long long offs)
 {
 }
 
@@ -624,9 +648,7 @@ static u64 timer_read(struct clocksource *cs)
 		 * to return from time_travel_update_time().
 		 */
 		if (!irqs_disabled() && !in_interrupt() && !in_softirq())
-			time_travel_update_time(time_travel_time +
-						TIMER_MULTIPLIER,
-						false);
+			time_travel_update_time_rel(TIMER_MULTIPLIER);
 		return time_travel_time / TIMER_MULTIPLIER;
 	}