Index: sys/arm64/arm64/exec_machdep.c
===================================================================
--- sys/arm64/arm64/exec_machdep.c
+++ sys/arm64/arm64/exec_machdep.c
@@ -60,6 +60,12 @@
 #include <machine/vfp.h>
 #endif
 
+_Static_assert(sizeof(mcontext_t) == 880, "mcontext_t bogusly changed size");
+#ifdef COMPAT_FREEBSD32
+_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 */
+
 static void get_fpcontext(struct thread *td, mcontext_t *mcp);
 static void set_fpcontext(struct thread *td, mcontext_t *mcp);