diff --git a/include/spinlock.h b/include/spinlock.h
index 15ff47677b5..33875d1f378 100644
--- a/include/spinlock.h
+++ b/include/spinlock.h
@@ -59,7 +59,7 @@ struct k_spinlock {
 	/* Stores the thread that holds the lock with the locking CPU
 	 * ID in the bottom two bits.
 	 */
-	size_t thread_cpu;
+	uintptr_t thread_cpu;
 #endif
 };
 
diff --git a/kernel/thread.c b/kernel/thread.c
index 51bb663879d..9a0ac2e60d6 100644
--- a/kernel/thread.c
+++ b/kernel/thread.c
@@ -727,7 +727,7 @@ bool z_spin_lock_valid(struct k_spinlock *l)
 
 bool z_spin_unlock_valid(struct k_spinlock *l)
 {
-	if (l->thread_cpu != (_current_cpu->id | (u32_t)_current)) {
+	if (l->thread_cpu != (_current_cpu->id | (uintptr_t)_current)) {
 		return false;
 	}
 	l->thread_cpu = 0;
@@ -736,7 +736,7 @@ bool z_spin_unlock_valid(struct k_spinlock *l)
 
 void z_spin_lock_set_owner(struct k_spinlock *l)
 {
-	l->thread_cpu = _current_cpu->id | (u32_t)_current;
+	l->thread_cpu = _current_cpu->id | (uintptr_t)_current;
 }
 
 #endif