diff --git a/libexec/tftpd/tests/Makefile b/libexec/tftpd/tests/Makefile
--- a/libexec/tftpd/tests/Makefile
+++ b/libexec/tftpd/tests/Makefile
@@ -4,6 +4,5 @@
 TEST_METADATA.functional+=	timeout=15
 
 LIBADD=	util
-CSTD=	c11
 
 .include <bsd.test.mk>
diff --git a/sbin/newfs_msdos/Makefile b/sbin/newfs_msdos/Makefile
--- a/sbin/newfs_msdos/Makefile
+++ b/sbin/newfs_msdos/Makefile
@@ -9,7 +9,6 @@
 .if ${MACHINE_CPUARCH} == "arm"
 WARNS?= 3
 .endif
-CSTD=	c11
 
 HAS_TESTS=
 SUBDIR.${MK_TESTS}+= tests
diff --git a/share/mk/bsd.sys.mk b/share/mk/bsd.sys.mk
--- a/share/mk/bsd.sys.mk
+++ b/share/mk/bsd.sys.mk
@@ -10,8 +10,7 @@
 
 .include <bsd.compiler.mk>
 
-# the default is gnu99 for now
-CSTD?=		gnu99
+CSTD?=		gnu17
 
 .if ${CSTD} == "c89" || ${CSTD} == "c90"
 CFLAGS+=	-std=iso9899:1990
diff --git a/usr.bin/sort/Makefile b/usr.bin/sort/Makefile
--- a/usr.bin/sort/Makefile
+++ b/usr.bin/sort/Makefile
@@ -3,7 +3,6 @@
 PACKAGE= runtime
 PROG=	sort
 SRCS=	bwstring.c coll.c file.c mem.c radixsort.c sort.c vsort.c
-CSTD=	c11
 
 sort.1: sort.1.in
 	sed ${MAN_SUB} ${.ALLSRC} >${.TARGET}
diff --git a/usr.bin/zstd/Makefile b/usr.bin/zstd/Makefile
--- a/usr.bin/zstd/Makefile
+++ b/usr.bin/zstd/Makefile
@@ -25,7 +25,6 @@
 	zstd.1 zstdcat.1 \
 	zstd.1 zstdmt.1
 
-CSTD=c11
 WARNS?=	2
 LIBADD=	zstd
 .PATH: ${SRCTOP}/sys/contrib/zstd/programs
diff --git a/usr.sbin/makefs/Makefile b/usr.sbin/makefs/Makefile
--- a/usr.sbin/makefs/Makefile
+++ b/usr.sbin/makefs/Makefile
@@ -15,7 +15,6 @@
 MAN=	makefs.8
 
 NO_WCAST_ALIGN=
-CSTD=	c11
 
 .if ${MK_ZFS} != "no"
 SRCS+=	zfs.c