diff --git a/doc/TODO.clang b/doc/TODO.clang
index dd3f1c6fddf0..79d383d209bd 100644
--- a/doc/TODO.clang
+++ b/doc/TODO.clang
@@ -1,4 +1,4 @@
-$NetBSD: TODO.clang,v 1.18 2016/02/27 18:50:39 joerg Exp $
+$NetBSD: TODO.clang,v 1.19 2016/02/27 21:42:14 joerg Exp $
 
 Hacks for the clang integration
 -------------------------------
@@ -14,3 +14,7 @@ macro (ab)use.
 
 src/tests/lib/libc/sync disables tests for atomics shorter than 32bit on
 SPARC64 due to missing codegen support.
+
+src/external/bsd/llvm/lib/libLLVMSupport and src/external/bsd/libc++/lib
+explicitly require -Wa,-Av8plus at the moment, because atomic ops are
+always lowered to CAS.
diff --git a/external/bsd/libc++/lib/Makefile b/external/bsd/libc++/lib/Makefile
index 4c5eb615c975..040ab1b719e4 100644
--- a/external/bsd/libc++/lib/Makefile
+++ b/external/bsd/libc++/lib/Makefile
@@ -1,4 +1,4 @@
-#	$NetBSD: Makefile,v 1.8 2016/01/05 13:07:46 christos Exp $
+#	$NetBSD: Makefile,v 1.9 2016/02/27 21:42:14 joerg Exp $
 
 LIB=		c++
 WARNS=		4
@@ -46,4 +46,8 @@ CWARNFLAGS.clang+=	-Wno-error=implicit-exception-spec-mismatch
 
 LDFLAGS+=	-Wl,-z,defs
 
+.if ${MACHINE_ARCH} == "sparc" || ${COMMON_MACHINE_ARCH:U} == "sparc"
+CXXFLAGS+=	${${ACTIVE_CC} == "clang":? -Wa,-Av8plus  :}
+.endif
+
 .include <bsd.lib.mk>
diff --git a/external/bsd/llvm/lib/libLLVMSupport/Makefile b/external/bsd/llvm/lib/libLLVMSupport/Makefile
index 057d45a2f2a6..9ae83cb8409c 100644
--- a/external/bsd/llvm/lib/libLLVMSupport/Makefile
+++ b/external/bsd/llvm/lib/libLLVMSupport/Makefile
@@ -1,4 +1,4 @@
-#	$NetBSD: Makefile,v 1.30 2015/01/29 20:41:36 joerg Exp $
+#	$NetBSD: Makefile,v 1.31 2016/02/27 21:42:14 joerg Exp $
 
 LIB=	LLVMSupport
 
@@ -118,6 +118,10 @@ SRCS+=	Host.inc \
 CPPFLAGS.${src}+=	-std=gnu99
 .endfor
 
+.if !defined(HOSTLIB) && ${MACHINE_ARCH} == "sparc"
+COPTS.Atomic.cpp+=	${${ACTIVE_CC} == "clang":? -Wa,-Av8plus :}
+.endif
+
 .if defined(HOSTLIB)
 .include <bsd.hostlib.mk>
 .else