diff --git a/lib/clang/llvm.build.mk b/lib/clang/llvm.build.mk
index 3a712cde1703..5aff7081fb76 100644
--- a/lib/clang/llvm.build.mk
+++ b/lib/clang/llvm.build.mk
@@ -111,10 +111,10 @@ CXXSTD?=	c++14
 CXXFLAGS+=	-fno-exceptions
 CXXFLAGS+=	-fno-rtti
 .if ${.MAKE.OS} == "FreeBSD" || !defined(BOOTSTRAPPING)
+CXXFLAGS.clang+= -stdlib=libc++
+.else
 # Building on macOS/Linux needs the real sysctl() not the bootstrap tools stub.
 CFLAGS+=	-DBOOTSTRAPPING_WANT_NATIVE_SYSCTL
-.else
-CXXFLAGS.clang+= -stdlib=libc++
 .endif
 .if defined(BOOTSTRAPPING) && ${.MAKE.OS} == "Linux"
 LIBADD+=	dl