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
@@ -954,6 +954,17 @@
 }
 #define	atomic_testandset_long	atomic_testandset_long
 
+static __inline int
+atomic_testandset_acq_long(volatile u_long *p, u_int v)
+{
+	int ret;
+
+	ret = atomic_testandset_32((volatile uint32_t *)p, v);
+	dmb();
+	return (ret);
+}
+#define	atomic_testandset_acq_long	atomic_testandset_acq_long
+
 static __inline int
 atomic_testandset_64(volatile uint64_t *p, u_int v)
 {
@@ -1098,7 +1109,6 @@
  * For:
  *  - atomic_load_acq_8
  *  - atomic_load_acq_16
- *  - atomic_testandset_acq_long
  */
 #include <sys/_atomic_subword.h>