diff --git a/embassy-nrf/src/time_driver.rs b/embassy-nrf/src/time_driver.rs
index 0f31c5c9c..b41169c01 100644
--- a/embassy-nrf/src/time_driver.rs
+++ b/embassy-nrf/src/time_driver.rs
@@ -1,11 +1,11 @@
 use core::cell::Cell;
 use core::{mem, ptr};
 
+use core::sync::atomic::{compiler_fence, AtomicU32, AtomicU8, Ordering};
 use critical_section::CriticalSection;
 use embassy_sync::blocking_mutex::raw::CriticalSectionRawMutex;
 use embassy_sync::blocking_mutex::CriticalSectionMutex as Mutex;
 use embassy_time_driver::{AlarmHandle, Driver};
-use portable_atomic::{compiler_fence, AtomicU32, AtomicU8, Ordering};
 
 use crate::interrupt::InterruptExt;
 use crate::{interrupt, pac};
@@ -171,7 +171,8 @@ impl RtcDriver {
     fn next_period(&self) {
         critical_section::with(|cs| {
             let r = rtc();
-            let period = self.period.fetch_add(1, Ordering::Relaxed) + 1;
+            let period = self.period.load(Ordering::Relaxed) + 1;
+            self.period.store(period, Ordering::Relaxed);
             let t = (period as u64) << 23;
 
             for n in 0..ALARM_COUNT {
@@ -219,18 +220,15 @@ impl Driver for RtcDriver {
     }
 
     unsafe fn allocate_alarm(&self) -> Option<AlarmHandle> {
-        let id = self.alarm_count.fetch_update(Ordering::AcqRel, Ordering::Acquire, |x| {
-            if x < ALARM_COUNT as u8 {
-                Some(x + 1)
+        critical_section::with(|_| {
+            let id = self.alarm_count.load(Ordering::Relaxed);
+            if id < ALARM_COUNT as u8 {
+                self.alarm_count.store(id + 1, Ordering::Relaxed);
+                Some(AlarmHandle::new(id))
             } else {
                 None
             }
-        });
-
-        match id {
-            Ok(id) => Some(AlarmHandle::new(id)),
-            Err(_) => None,
-        }
+        })
     }
 
     fn set_alarm_callback(&self, alarm: AlarmHandle, callback: fn(*mut ()), ctx: *mut ()) {