Index: sys/arm64/include/ucontext.h
===================================================================
--- sys/arm64/include/ucontext.h
+++ sys/arm64/include/ucontext.h
@@ -60,6 +60,7 @@
 };
 
 typedef struct __mcontext mcontext_t;
+_Static_assert(sizeof(mcontext_t) == 880, "mcontext_t bogusly changed size");
 
 #ifdef COMPAT_FREEBSD32
 #include <compat/freebsd32/freebsd32_signal.h>
@@ -84,6 +85,10 @@
 	__uint32_t	mcv_fpscr;
 } mcontext32_vfp_t;
 
+_Static_assert(sizeof(mcontext32_t) == 208, "mcontext32_t bogusly changed size");
+_Static_assert(sizeof(ucontext32_t) == 260, "ucontext32_t bogusly changed size");
+
+
 #endif /* COMPAT_FREEBSD32 */
 
 #endif	/* !_MACHINE_UCONTEXT_H_ */