diff --git a/lib/clang/llvm.build.mk b/lib/clang/llvm.build.mk
index c731deba897..e88b2ff1033 100644
--- a/lib/clang/llvm.build.mk
+++ b/lib/clang/llvm.build.mk
@@ -119,6 +119,7 @@ LDFLAGS+=	-Wl,-m,elf64lriscv_fbsd
 .endif
 .endif
 
+CXXSTD=		c++17
 CXXFLAGS+=	-fno-exceptions
 CXXFLAGS+=	-fno-rtti
 .if ${.MAKE.OS} == "FreeBSD" || !defined(BOOTSTRAPPING)
diff --git a/lib/libclang_rt/Makefile.inc b/lib/libclang_rt/Makefile.inc
index e7db5a46966..c472e8b741b 100644
--- a/lib/libclang_rt/Makefile.inc
+++ b/lib/libclang_rt/Makefile.inc
@@ -33,3 +33,4 @@ CXXFLAGS+=	-fvisibility-inlines-hidden
 CXXFLAGS+=	-fvisibility=hidden
 CFLAGS+=	-I${CRTSRC}/include
 CFLAGS+=	-I${CRTSRC}/lib
+CXXSTD=		c++17
diff --git a/lib/libomp/Makefile b/lib/libomp/Makefile
index f1513e70f3f..6c14c7d2107 100644
--- a/lib/libomp/Makefile
+++ b/lib/libomp/Makefile
@@ -57,6 +57,7 @@ CFLAGS+=	-fdata-sections
 CXXFLAGS+=	-fvisibility-inlines-hidden
 CXXFLAGS+=	-fno-exceptions
 CXXFLAGS+=	-fno-rtti
+CXXSTD=		c++17
 
 .if ${COMPILER_TYPE} == "clang"
 .if ${MACHINE_CPUARCH} == "i386"