diff --git a/sys/ztimer/overhead.c b/sys/ztimer/overhead.c
index c472a150f0..9744a36a06 100644
--- a/sys/ztimer/overhead.c
+++ b/sys/ztimer/overhead.c
@@ -43,18 +43,21 @@ int32_t ztimer_overhead_set(ztimer_clock_t *clock, uint32_t base)
     callback_arg_t arg = { .clock = clock, .val = &after };
     ztimer_t t = { .callback = _callback, .arg = &arg };
 
+    ztimer_acquire(clock);
     pre = ztimer_now(clock);
     ztimer_set(clock, &t, base);
     while (!after) {}
+    ztimer_release(clock);
     return after - pre - base;
 }
 
 int32_t ztimer_overhead_sleep(ztimer_clock_t *clock, uint32_t base)
 {
+    ztimer_acquire(clock);
     uint32_t pre = ztimer_now(clock);
-
     ztimer_sleep(clock, base);
     uint32_t after = ztimer_now(clock);
+    ztimer_release(clock);
 
     return after - pre - base;
 }