diff --git a/sys/arm64/arm64/exec_machdep.c b/sys/arm64/arm64/exec_machdep.c
--- a/sys/arm64/arm64/exec_machdep.c
+++ b/sys/arm64/arm64/exec_machdep.c
@@ -60,6 +60,10 @@
 #include <machine/vfp.h>
 #endif
 
+_Static_assert(sizeof(mcontext_t) == 880, "mcontext_t size incorrect");
+_Static_assert(sizeof(ucontext_t) == 960, "ucontext_t size incorrect");
+_Static_assert(sizeof(siginfo_t) == 80, "siginfo_t size incorrect");
+
 static void get_fpcontext(struct thread *td, mcontext_t *mcp);
 static void set_fpcontext(struct thread *td, mcontext_t *mcp);
 
diff --git a/sys/arm64/arm64/freebsd32_machdep.c b/sys/arm64/arm64/freebsd32_machdep.c
--- a/sys/arm64/arm64/freebsd32_machdep.c
+++ b/sys/arm64/arm64/freebsd32_machdep.c
@@ -48,6 +48,10 @@
 #include <vm/pmap.h>
 #include <vm/vm_map.h>
 
+_Static_assert(sizeof(mcontext32_t) == 208, "mcontext32_t size incorrect");
+_Static_assert(sizeof(ucontext32_t) == 260, "ucontext32_t size incorrect");
+_Static_assert(sizeof(struct siginfo32) == 64, "struct siginfo32 size incorrect");
+
 extern void freebsd32_sendsig(sig_t catcher, ksiginfo_t *ksi, sigset_t *mask);
 
 /*