diff --git a/sys/arm/include/atomic.h b/sys/arm/include/atomic.h
--- a/sys/arm/include/atomic.h
+++ b/sys/arm/include/atomic.h
@@ -93,6 +93,12 @@
 #define atomic_store_rel_int		atomic_store_rel_32
 #define atomic_swap_int			atomic_swap_32
 
+/*
+ * For:
+ *  - atomic_load_acq_8
+ *  - atomic_load_acq_16
+ *  - atomic_testandset_acq_long
+ */
 #include <sys/_atomic_subword.h>
 
 #endif /* _MACHINE_ATOMIC_H_ */