diff --git a/sys/i386/include/atomic.h b/sys/i386/include/atomic.h
index c167cf5c0fa..7cd5b0d2a7e 100644
--- a/sys/i386/include/atomic.h
+++ b/sys/i386/include/atomic.h
@@ -129,6 +129,7 @@ int		atomic_cmpset_64(volatile uint64_t *, uint64_t, uint64_t);
 uint64_t	atomic_load_acq_64(volatile uint64_t *);
 void		atomic_store_rel_64(volatile uint64_t *, uint64_t);
 uint64_t	atomic_swap_64(volatile uint64_t *, uint64_t);
+uint64_t	atomic_fetchadd_64(volatile uint64_t *, uint64_t);
 
 #else /* !KLD_MODULE && __GNUCLIKE_ASM */
 
@@ -565,6 +566,17 @@ atomic_swap_64(volatile uint64_t *p, uint64_t v)
 		return (atomic_swap_64_i586(p, v));
 }
 
+static __inline uint64_t
+atomic_fetchadd_64(volatile uint64_t *p, uint64_t v)
+{
+
+	for (;;) {
+		uint64_t t = *p;
+		if (atomic_cmpset_64(p, t, t + v))
+			return (t);
+	}
+}
+
 #endif /* _KERNEL */
 
 #endif /* KLD_MODULE || !__GNUCLIKE_ASM */