diff --git a/sys/alpha/include/ucontext.h b/sys/alpha/include/ucontext.h
index 2c3ed7053a7..d60cc6c3523 100644
--- a/sys/alpha/include/ucontext.h
+++ b/sys/alpha/include/ucontext.h
@@ -50,7 +50,8 @@ typedef struct __mcontext {
 #define	_MC_REV0_SIGFRAME	1	/* context is a signal frame */
 #define	_MC_REV0_TRAPFRAME	2	/* context is a trap frame */
 	long	mc_format;
-	long	mc_spare[6];
+	long	mc_thrptr;		/* Thread pointer */
+	long	mc_spare[5];
 } mcontext_t;
 
 #if defined(_KERNEL) && defined(COMPAT_FREEBSD4)