diff --git a/arch/sim/src/sim/up_testset.c b/arch/sim/src/sim/up_testset.c
index a8dc66077cf..79b84e13777 100644
--- a/arch/sim/src/sim/up_testset.c
+++ b/arch/sim/src/sim/up_testset.c
@@ -74,7 +74,7 @@ uint8_t up_testset(volatile uint8_t *lock)
    * following test and set is atomic.
    */
 
-  return atomic_exchange(lock, 1);
+  return atomic_exchange((_Atomic uint8_t *)lock, 1);
 #else
 
   /* In the non-SMP case, the simulation is implemented with a single thread