diff --git a/sys/arch/sparc64/sparc64/compat_13_machdep.c b/sys/arch/sparc64/sparc64/compat_13_machdep.c
index 2d844d0fed99..6f46bc9e96df 100644
--- a/sys/arch/sparc64/sparc64/compat_13_machdep.c
+++ b/sys/arch/sparc64/sparc64/compat_13_machdep.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: compat_13_machdep.c,v 1.2 1998/10/08 02:31:40 eeh Exp $	*/
+/*	$NetBSD: compat_13_machdep.c,v 1.3 1998/11/16 06:51:35 eeh Exp $	*/
 
 /*-
  * Copyright (c) 1996, 1997, 1998 The NetBSD Foundation, Inc.
@@ -91,7 +91,14 @@ compat_13_sys_sigreturn(p, v, retval)
 	 * verified.  pc and npc must be multiples of 4.  This is all
 	 * that is required; if it holds, just do it.
 	 */
-	if (((scp->sc_pc | scp->sc_npc) & 3) != 0)
+	if (((scp->sc_pc | scp->sc_npc) & 3) != 0 || scp->sc_pc == 0 || scp->sc_npc == 0)
+#ifdef DEBUG
+	{
+		printf("sigreturn13: pc %p or npc %p invalid\n", scp->sc_pc, scp->sc_npc);
+		Debugger();
+		return (EINVAL);
+	}
+#endif
 		return (EINVAL);
 	/* take only psr ICC field */
 #ifdef _LP64
diff --git a/sys/arch/sparc64/sparc64/locore.s b/sys/arch/sparc64/sparc64/locore.s
index 7e19f67b6d22..42e989c0c49e 100644
--- a/sys/arch/sparc64/sparc64/locore.s
+++ b/sys/arch/sparc64/sparc64/locore.s
@@ -3936,10 +3936,10 @@ zshard:
  */
 return_from_trap:
 #ifdef DEBUG
-	!! Make sure we don't have pc == npc or we suck.
+	!! Make sure we don't have pc == npc == 0 or we suck.
 	ldx	[%sp + CC64FSZ + STKB + TF_PC], %g2
 	ldx	[%sp + CC64FSZ + STKB + TF_NPC], %g3
-	cmp	%g2, %g3
+	orcc	%g2, %g3, %g0
 	tz	%icc, 1
 #endif
 #ifdef NOTDEF_DEBUG
diff --git a/sys/arch/sparc64/sparc64/machdep.c b/sys/arch/sparc64/sparc64/machdep.c
index f161fbb99f0c..0453c9e1b9e6 100644
--- a/sys/arch/sparc64/sparc64/machdep.c
+++ b/sys/arch/sparc64/sparc64/machdep.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: machdep.c,v 1.21 1998/10/19 22:09:20 tron Exp $ */
+/*	$NetBSD: machdep.c,v 1.22 1998/11/16 06:51:36 eeh Exp $ */
 
 /*-
  * Copyright (c) 1996, 1997, 1998 The NetBSD Foundation, Inc.
@@ -645,7 +645,7 @@ sendsig(catcher, sig, mask, code)
 	/*
 	 * Build the signal context to be used by sigreturn.
 	 */
-	sf.sf_sc.sc_onstack = onstack;
+	sf.sf_sc.sc_onstack = psp->ps_sigstk.ss_flags & SS_ONSTACK;
 	sf.sf_sc.sc_mask = *mask;
 #ifdef COMPAT_13
 	/*
@@ -674,7 +674,7 @@ sendsig(catcher, sig, mask, code)
 	 * joins seamlessly with the frame it was in when the signal occurred,
 	 * so that the debugger and _longjmp code can back up through it.
 	 */
-	newsp = (struct rwindow *)((vaddr_t)fp - CC64FSZ);
+	newsp = (struct rwindow *)((vaddr_t)fp - sizeof(struct rwindow));
 	write_user_windows();
 #ifdef DEBUG
 	if ((sigdebug & SDB_KSTACK))
@@ -794,10 +794,10 @@ sys___sigreturn14(p, v, retval)
 	 * verified.  pc and npc must be multiples of 4.  This is all
 	 * that is required; if it holds, just do it.
 	 */
-	if (((sc.sc_pc | sc.sc_npc) & 3) != 0)
+	if (((sc.sc_pc | sc.sc_npc) & 3) != 0 || (sc.sc_pc == 0) || (sc.sc_npc == 0))
 #ifdef DEBUG
 	{
-		printf("sigreturn: pc %p or npc %p invalid\n", sc.sc_pc, sc.sc_npc);
+		printf("sigreturn14: pc %p or npc %p invalid\n", sc.sc_pc, sc.sc_npc);
 		Debugger();
 		return (EINVAL);
 	}
diff --git a/sys/arch/sparc64/sparc64/sunos_machdep.c b/sys/arch/sparc64/sparc64/sunos_machdep.c
index fcf6e6a39207..b7c320f1a83f 100644
--- a/sys/arch/sparc64/sparc64/sunos_machdep.c
+++ b/sys/arch/sparc64/sparc64/sunos_machdep.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: sunos_machdep.c,v 1.4 1998/10/08 02:31:41 eeh Exp $	*/
+/*	$NetBSD: sunos_machdep.c,v 1.5 1998/11/16 06:51:36 eeh Exp $	*/
 
 /*
  * Copyright (c) 1995 Matthew R. Green
@@ -237,7 +237,14 @@ sunos_sys_sigreturn(p, v, retval)
 	 * verified.  pc and npc must be multiples of 4.  This is all
 	 * that is required; if it holds, just do it.
 	 */
-	if (((scp->sc_pc | scp->sc_npc) & 3) != 0)
+	if (((scp->sc_pc | scp->sc_npc) & 3) != 0 || scp->sc_pc == 0 || scp->sc_npc == 0)
+#ifdef DEBUG
+	{
+		printf("sigreturn13: pc %p or npc %p invalid\n", scp->sc_pc, scp->sc_npc);
+		Debugger();
+		return (EINVAL);
+	}
+#endif
 		return (EINVAL);
 	/* take only psr ICC field */
 	tf->tf_tstate = (int64_t)(tf->tf_tstate & ~TSTATE_CCR) | PSRCC_TO_TSTATE(scp->sc_psr);