Index: sys/riscv/riscv/exec_machdep.c
===================================================================
--- sys/riscv/riscv/exec_machdep.c
+++ sys/riscv/riscv/exec_machdep.c
@@ -77,6 +77,9 @@
 static void get_fpcontext(struct thread *td, mcontext_t *mcp);
 static void set_fpcontext(struct thread *td, mcontext_t *mcp);
 
+_Static_assert(sizeof(mcontext_t) == 864, "mcontext_t bogusly changed size");
+_Static_assert(sizeof(ucontext_t) == 936, "mcontext_t bogusly changed size");
+
 int
 fill_regs(struct thread *td, struct reg *regs)
 {