diff --git a/drivers/timer/npcx_itim_timer.c b/drivers/timer/npcx_itim_timer.c
index e1c83a29980..ca6788d7a28 100644
--- a/drivers/timer/npcx_itim_timer.c
+++ b/drivers/timer/npcx_itim_timer.c
@@ -249,12 +249,12 @@ uint32_t sys_clock_elapsed(void)
 	}
 
 	k_spinlock_key_t key = k_spin_lock(&lock);
-	uint64_t current = npcx_itim_get_sys_cyc64();
+	uint64_t delta_cycle = npcx_itim_get_sys_cyc64() - cyc_sys_announced;
 
 	k_spin_unlock(&lock, key);
 
 	/* Return how many ticks elapsed since last sys_clock_announce() call */
-	return (uint32_t)((current - cyc_sys_announced) / SYS_CYCLES_PER_TICK);
+	return (uint32_t)(delta_cycle / SYS_CYCLES_PER_TICK);
 }
 
 uint32_t sys_clock_cycle_get_32(void)
diff --git a/dts/arm/nuvoton/npcx7.dtsi b/dts/arm/nuvoton/npcx7.dtsi
index 97e650a0764..8f2e80c0d13 100644
--- a/dts/arm/nuvoton/npcx7.dtsi
+++ b/dts/arm/nuvoton/npcx7.dtsi
@@ -68,7 +68,7 @@
 			reg-names = "evt_itim", "sys_itim";
 			clocks = <&pcc NPCX_CLOCK_BUS_LFCLK NPCX_PWDWN_CTL4 3
 				  &pcc NPCX_CLOCK_BUS_APB2 NPCX_PWDWN_CTL7 5>;
-			interrupts = <46 2>; /* Event timer interrupt */
+			interrupts = <46 1>; /* Event timer interrupt */
 			label = "ITIM";
 		};
 
diff --git a/dts/arm/nuvoton/npcx9.dtsi b/dts/arm/nuvoton/npcx9.dtsi
index d05921309b2..296be5a2ba6 100644
--- a/dts/arm/nuvoton/npcx9.dtsi
+++ b/dts/arm/nuvoton/npcx9.dtsi
@@ -69,7 +69,7 @@
 			reg-names = "evt_itim", "sys_itim";
 			clocks = <&pcc NPCX_CLOCK_BUS_LFCLK NPCX_PWDWN_CTL4 0
 				  &pcc NPCX_CLOCK_BUS_APB2 NPCX_PWDWN_CTL7 5>;
-			interrupts = <28 2>; /* Event timer interrupt */
+			interrupts = <28 1>; /* Event timer interrupt */
 			label = "ITIM";
 		};