Index: sys/i386/i386/exec_machdep.c
===================================================================
--- sys/i386/i386/exec_machdep.c
+++ sys/i386/i386/exec_machdep.c
@@ -115,6 +115,9 @@
 
 extern struct sysentvec elf32_freebsd_sysvec;
 
+_Static_assert(sizeof(mcontext_t) == 640, "mcontext_t bogusly changed size");
+_Static_assert(sizeof(ucontext_t) == 704, "ucontext_t bogusly changed size");
+
 /*
  * Send an interrupt to process.
  *