diff --git a/lib/libc++/Makefile b/lib/libc++/Makefile
index 6e95823677e3..26877eebe51b 100644
--- a/lib/libc++/Makefile
+++ b/lib/libc++/Makefile
@@ -53,7 +53,9 @@ cxxrt_${_S}:
 
 WARNS=		0
 CFLAGS+=	-I${HDRDIR} -I${LIBCXXRTDIR} -nostdlib -DLIBCXXRT
+.if !defined(CXXFLAGS) || ${CXXFLAGS:M-std=*}" == ""
 CXXFLAGS+=	-std=c++0x
+.endif
 
 DPADD=		${LIBCXXRT}
 LDADD=		-lcxxrt