diff --git a/sys/compat/linuxkpi/common/include/linux/build_bug.h b/sys/compat/linuxkpi/common/include/linux/build_bug.h
--- a/sys/compat/linuxkpi/common/include/linux/build_bug.h
+++ b/sys/compat/linuxkpi/common/include/linux/build_bug.h
@@ -59,7 +59,4 @@
 #define	BUILD_BUG_ON_INVALID(expr)	while (0) { (void)(expr); }
 #define	BUILD_BUG_ON_ZERO(x)	((int)sizeof(struct { int:-((x) != 0); }))
 
-#define static_assert(x, ...)		__static_assert(x, ##__VA_ARGS__, #x)
-#define __static_assert(x, msg, ...)	_Static_assert(x, msg)
-
 #endif
diff --git a/sys/conf/kern.mk b/sys/conf/kern.mk
--- a/sys/conf/kern.mk
+++ b/sys/conf/kern.mk
@@ -282,7 +282,7 @@
 .PHONY: ${PHONY_NOTMAIN}
 .NOTMAIN: ${PHONY_NOTMAIN}
 
-CSTD?=		gnu99
+CSTD?=		gnu17
 
 .if ${CSTD} == "k&r"
 CFLAGS+=        -traditional
diff --git a/sys/contrib/zstd/lib/freebsd/assert.h b/sys/contrib/zstd/lib/freebsd/assert.h
new file mode 100644
--- /dev/null
+++ b/sys/contrib/zstd/lib/freebsd/assert.h
@@ -0,0 +1,2 @@
+/* This file is in the public domain */
+#include <sys/systm.h>
diff --git a/sys/sys/systm.h b/sys/sys/systm.h
--- a/sys/sys/systm.h
+++ b/sys/sys/systm.h
@@ -590,6 +590,9 @@
 #define	__witness_used	__unused
 #endif
 
+#define static_assert(x, ...)		__static_assert(x, ##__VA_ARGS__, #x)
+#define __static_assert(x, msg, ...)	_Static_assert(x, msg)
+
 #endif /* _KERNEL */
 
 __NULLABILITY_PRAGMA_POP