diff --git a/sys/sparc64/include/asmacros.h b/sys/sparc64/include/asmacros.h
index 840959fa803..777b35a4d18 100644
--- a/sys/sparc64/include/asmacros.h
+++ b/sys/sparc64/include/asmacros.h
@@ -90,6 +90,17 @@
 	bne,pn	%icc, 9b ; \
 	 mov	r3, r2
 
+/*
+ * Atomically clear a number of bits of an u_long in memory.
+ */
+#define	ATOMIC_CLEAR_LONG(r1, r2, r3, bits) \
+	ldx	[r1], r2 ; \
+9:	andn	r2, bits, r3 ; \
+	casxa	[r1] ASI_N, r2, r3 ; \
+	cmp	r2, r3 ; \
+	bne,pn	%icc, 9b ; \
+	 mov	r3, r2
+
 #define	PCPU(member)	PCPU_REG + PC_ ## member
 #define	PCPU_ADDR(member, reg) \
 	add	PCPU_REG, PC_ ## member, reg