Index: sys/arm/arm/exec_machdep.c
===================================================================
--- sys/arm/arm/exec_machdep.c
+++ sys/arm/arm/exec_machdep.c
@@ -69,6 +69,10 @@
 #include <vm/pmap.h>
 #include <vm/vm_map.h>
 
+_Static_assert(sizeof(mcontext_t) == 208, "mcontext_t bogusly changed size");
+_Static_assert(sizeof(ucontext_t) == 260, "ucontext_t bogusly changed size");
+_Static_assert(sizeof(siginfo_t) == 64, "siginfo_t bogusly changed size");
+
 /*
  * Clear registers on exec
  */