diff --git a/libc/include/sys/ucontext.h b/libc/include/sys/ucontext.h
index f29381bf6..3737cbec5 100644
--- a/libc/include/sys/ucontext.h
+++ b/libc/include/sys/ucontext.h
@@ -243,7 +243,7 @@ typedef struct user_i387_struct* fpregset_t;
 typedef struct {
   gregset_t gregs;
   fpregset_t fpregs;
-  /* TODO: reserved space? */
+  unsigned long __reserved1[8];
 } mcontext_t;
 
 typedef struct ucontext {