diff --git a/src/pkg/runtime/os_openbsd.h b/src/pkg/runtime/os_openbsd.h
index 4ecf78d882..b2d79e7f99 100644
--- a/src/pkg/runtime/os_openbsd.h
+++ b/src/pkg/runtime/os_openbsd.h
@@ -5,17 +5,22 @@
 #define SIG_DFL ((void*)0)
 #define SIG_IGN ((void*)1)
 
+#define SIG_BLOCK 1
+#define SIG_UNBLOCK 2
+#define SIG_SETMASK 3
+
 struct sigaction;
 
-void	runtime·sigpanic(void);
-void	runtime·sigaltstack(Sigaltstack*, Sigaltstack*);
-void	runtime·sigaction(int32, struct sigaction*, struct sigaction*);
-void	runtime·setsig(int32, void(*)(int32, Siginfo*, void*, G*), bool);
-void	runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp);
-void	runtime·setitimer(int32, Itimerval*, Itimerval*);
-int32	runtime·sysctl(uint32*, uint32, byte*, uintptr*, byte*, uintptr);
-
 void	runtime·raisesigpipe(void);
+void	runtime·setsig(int32, void(*)(int32, Siginfo*, void*, G*), bool);
+void	runtime·sigpanic(void);
+
+void	runtime·setitimer(int32, Itimerval*, Itimerval*);
+void	runtime·sigaction(int32, struct sigaction*, struct sigaction*);
+void	runtime·sigaltstack(Sigaltstack*, Sigaltstack*);
+void	runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp);
+Sigset	runtime·sigprocmask(int32, Sigset);
+int32	runtime·sysctl(uint32*, uint32, byte*, uintptr*, byte*, uintptr);
 
 #define	NSIG 33
 #define	SI_USER	0
diff --git a/src/pkg/runtime/signal_openbsd_amd64.c b/src/pkg/runtime/signal_openbsd_amd64.c
index 8b4f624e7c..2f47ffc843 100644
--- a/src/pkg/runtime/signal_openbsd_amd64.c
+++ b/src/pkg/runtime/signal_openbsd_amd64.c
@@ -70,8 +70,8 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 		gp->sigcode1 = *(uintptr*)((byte*)info + 16); /* si_addr */
 		gp->sigpc = r->sc_rip;
 
-		// Only push runtime·sigpanic if r->mc_rip != 0.
-		// If r->mc_rip == 0, probably panicked because of a
+		// Only push runtime·sigpanic if r->sc_rip != 0.
+		// If r->sc_rip == 0, probably panicked because of a
 		// call to a nil func.  Not pushing that onto sp will
 		// make the trace look like a call to runtime·sigpanic instead.
 		// (Otherwise the trace will end at runtime·sigpanic and we
@@ -133,8 +133,8 @@ runtime·setsig(int32 i, void (*fn)(int32, Siginfo*, void*, G*), bool restart)
 	sa.sa_flags = SA_SIGINFO|SA_ONSTACK;
 	if(restart)
 		sa.sa_flags |= SA_RESTART;
-	sa.sa_mask = ~0ULL;
-	if (fn == runtime·sighandler)
+	sa.sa_mask = ~0U;
+	if(fn == runtime·sighandler)
 		fn = (void*)runtime·sigtramp;
 	sa.__sigaction_u.__sa_sigaction = (void*)fn;
 	runtime·sigaction(i, &sa, nil);
diff --git a/src/pkg/runtime/signals_openbsd.h b/src/pkg/runtime/signals_openbsd.h
index 4d27e050d0..7140de86fc 100644
--- a/src/pkg/runtime/signals_openbsd.h
+++ b/src/pkg/runtime/signals_openbsd.h
@@ -9,16 +9,16 @@
 #define D SigDefault
 
 SigTab runtime·sigtab[] = {
-	/* 0 */	0, "SIGNONE: no trap",
-	/* 1 */	N+K, "SIGHUP: terminal line hangup",
-	/* 2 */	N+K, "SIGINT: interrupt",
-	/* 3 */	N+T, "SIGQUIT: quit",
-	/* 4 */	T, "SIGILL: illegal instruction",
-	/* 5 */	T, "SIGTRAP: trace trap",
-	/* 6 */	N+T, "SIGABRT: abort",
-	/* 7 */	T, "SIGEMT: emulate instruction executed",
-	/* 8 */	P, "SIGFPE: floating-point exception",
-	/* 9 */	0, "SIGKILL: kill",
+	/*  0 */	0, "SIGNONE: no trap",
+	/*  1 */	N+K, "SIGHUP: terminal line hangup",
+	/*  2 */	N+K, "SIGINT: interrupt",
+	/*  3 */	N+T, "SIGQUIT: quit",
+	/*  4 */	T, "SIGILL: illegal instruction",
+	/*  5 */	T, "SIGTRAP: trace trap",
+	/*  6 */	N+T, "SIGABRT: abort",
+	/*  7 */	T, "SIGEMT: emulate instruction executed",
+	/*  8 */	P, "SIGFPE: floating-point exception",
+	/*  9 */	0, "SIGKILL: kill",
 	/* 10 */	P, "SIGBUS: bus error",
 	/* 11 */	P, "SIGSEGV: segmentation violation",
 	/* 12 */	T, "SIGSYS: bad system call",
diff --git a/src/pkg/runtime/sys_openbsd_386.s b/src/pkg/runtime/sys_openbsd_386.s
index 593b4a9df2..22505c4f02 100644
--- a/src/pkg/runtime/sys_openbsd_386.s
+++ b/src/pkg/runtime/sys_openbsd_386.s
@@ -135,6 +135,14 @@ TEXT runtime·sigaction(SB),7,$-4
 	MOVL	$0xf1, 0xf1  // crash
 	RET
 
+TEXT runtime·sigprocmask(SB),7,$-4
+	MOVL	$48, AX			// sys_sigprocmask
+	INT	$0x80
+	JAE	2(PC)
+	MOVL	$0xf1, 0xf1  // crash
+	MOVL	AX, oset+0(FP)
+	RET
+
 TEXT runtime·sigtramp(SB),7,$44
 	get_tls(CX)
 
diff --git a/src/pkg/runtime/sys_openbsd_amd64.s b/src/pkg/runtime/sys_openbsd_amd64.s
index d2d48e6b56..0c7093dd5c 100644
--- a/src/pkg/runtime/sys_openbsd_amd64.s
+++ b/src/pkg/runtime/sys_openbsd_amd64.s
@@ -173,6 +173,16 @@ TEXT runtime·sigaction(SB),7,$-8
 	MOVL	$0xf1, 0xf1  // crash
 	RET
 
+TEXT runtime·sigprocmask(SB),7,$0
+	MOVL	8(SP), DI		// arg 1 - how
+	MOVL	12(SP), SI		// arg 2 - set
+	MOVL	$48, AX			// sys_sigprocmask
+	SYSCALL
+	JCC	2(PC)
+	MOVL	$0xf1, 0xf1  // crash
+	MOVL	AX, oset+0(FP)		// Return oset
+	RET
+
 TEXT runtime·sigtramp(SB),7,$64
 	get_tls(BX)
 	
diff --git a/src/pkg/runtime/thread_openbsd.c b/src/pkg/runtime/thread_openbsd.c
index d0f9472106..d9ce6d6028 100644
--- a/src/pkg/runtime/thread_openbsd.c
+++ b/src/pkg/runtime/thread_openbsd.c
@@ -20,6 +20,9 @@ enum
 
 extern SigTab runtime·sigtab[];
 
+static Sigset sigset_all = ~(Sigset)0;
+static Sigset sigset_none;
+
 extern int64 runtime·rfork_thread(int32 flags, void *stack, M *m, G *g, void (*fn)(void));
 extern int32 runtime·thrsleep(void *ident, int32 clock_id, void *tsp, void *lock);
 extern int32 runtime·thrwakeup(void *ident, int32 n);
@@ -128,6 +131,7 @@ runtime·semawakeup(M *mp)
 void
 runtime·newosproc(M *m, G *g, void *stk, void (*fn)(void))
 {
+	Sigset oset;
 	int32 flags;
 	int32 ret;
 
@@ -141,7 +145,11 @@ runtime·newosproc(M *m, G *g, void *stk, void (*fn)(void))
 
 	m->tls[0] = m->id;	// so 386 asm can find it
 
-	if((ret = runtime·rfork_thread(flags, stk, m, g, fn)) < 0) {
+	oset = runtime·sigprocmask(SIG_SETMASK, sigset_all);
+	ret = runtime·rfork_thread(flags, stk, m, g, fn);
+	runtime·sigprocmask(SIG_SETMASK, oset);
+
+	if(ret < 0) {
 		runtime·printf("runtime: failed to create new OS thread (have %d already; errno=%d)\n", runtime·mcount() - 1, -ret);
 		if (ret == -ENOTSUP)
 			runtime·printf("runtime: is kern.rthreads disabled?\n");
@@ -168,6 +176,7 @@ runtime·minit(void)
 	// Initialize signal handling
 	m->gsignal = runtime·malg(32*1024);
 	runtime·signalstack(m->gsignal->stackguard - StackGuard, 32*1024);
+	runtime·sigprocmask(SIG_SETMASK, sigset_none);
 }
 
 void