diff --git a/src/runtime/netpoll_aix.go b/src/runtime/netpoll_aix.go
index 22cc5138815..5247e56373a 100644
--- a/src/runtime/netpoll_aix.go
+++ b/src/runtime/netpoll_aix.go
@@ -135,10 +135,13 @@ func netpollarm(pd *pollDesc, mode int) {
 
 // netpollBreak interrupts a poll.
 func netpollBreak() {
-	if atomic.Cas(&netpollWakeSig, 0, 1) {
-		b := [1]byte{0}
-		write(uintptr(wrwake), unsafe.Pointer(&b[0]), 1)
+	// Failing to cas indicates there is an in-flight wakeup, so we're done here.
+	if !atomic.Cas(&netpollWakeSig, 0, 1) {
+		return
 	}
+
+	b := [1]byte{0}
+	write(uintptr(wrwake), unsafe.Pointer(&b[0]), 1)
 }
 
 // netpoll checks for ready network connections.
diff --git a/src/runtime/netpoll_epoll.go b/src/runtime/netpoll_epoll.go
index b7d61999659..7ad2c8ab35e 100644
--- a/src/runtime/netpoll_epoll.go
+++ b/src/runtime/netpoll_epoll.go
@@ -79,22 +79,25 @@ func netpollarm(pd *pollDesc, mode int) {
 
 // netpollBreak interrupts an epollwait.
 func netpollBreak() {
-	if atomic.Cas(&netpollWakeSig, 0, 1) {
-		for {
-			var b byte
-			n := write(netpollBreakWr, unsafe.Pointer(&b), 1)
-			if n == 1 {
-				break
-			}
-			if n == -_EINTR {
-				continue
-			}
-			if n == -_EAGAIN {
-				return
-			}
-			println("runtime: netpollBreak write failed with", -n)
-			throw("runtime: netpollBreak write failed")
+	// Failing to cas indicates there is an in-flight wakeup, so we're done here.
+	if !atomic.Cas(&netpollWakeSig, 0, 1) {
+		return
+	}
+
+	for {
+		var b byte
+		n := write(netpollBreakWr, unsafe.Pointer(&b), 1)
+		if n == 1 {
+			break
 		}
+		if n == -_EINTR {
+			continue
+		}
+		if n == -_EAGAIN {
+			return
+		}
+		println("runtime: netpollBreak write failed with", -n)
+		throw("runtime: netpollBreak write failed")
 	}
 }
 
diff --git a/src/runtime/netpoll_kqueue.go b/src/runtime/netpoll_kqueue.go
index 1694753b6fe..78d1663ad9a 100644
--- a/src/runtime/netpoll_kqueue.go
+++ b/src/runtime/netpoll_kqueue.go
@@ -83,19 +83,22 @@ func netpollarm(pd *pollDesc, mode int) {
 
 // netpollBreak interrupts a kevent.
 func netpollBreak() {
-	if atomic.Cas(&netpollWakeSig, 0, 1) {
-		for {
-			var b byte
-			n := write(netpollBreakWr, unsafe.Pointer(&b), 1)
-			if n == 1 || n == -_EAGAIN {
-				break
-			}
-			if n == -_EINTR {
-				continue
-			}
-			println("runtime: netpollBreak write failed with", -n)
-			throw("runtime: netpollBreak write failed")
+	// Failing to cas indicates there is an in-flight wakeup, so we're done here.
+	if !atomic.Cas(&netpollWakeSig, 0, 1) {
+		return
+	}
+
+	for {
+		var b byte
+		n := write(netpollBreakWr, unsafe.Pointer(&b), 1)
+		if n == 1 || n == -_EAGAIN {
+			break
 		}
+		if n == -_EINTR {
+			continue
+		}
+		println("runtime: netpollBreak write failed with", -n)
+		throw("runtime: netpollBreak write failed")
 	}
 }
 
diff --git a/src/runtime/netpoll_solaris.go b/src/runtime/netpoll_solaris.go
index 6e545b3d31b..ec51771b579 100644
--- a/src/runtime/netpoll_solaris.go
+++ b/src/runtime/netpoll_solaris.go
@@ -191,17 +191,20 @@ func netpollarm(pd *pollDesc, mode int) {
 
 // netpollBreak interrupts a port_getn wait.
 func netpollBreak() {
-	if atomic.Cas(&netpollWakeSig, 0, 1) {
-		// Use port_alert to put portfd into alert mode.
-		// This will wake up all threads sleeping in port_getn on portfd,
-		// and cause their calls to port_getn to return immediately.
-		// Further, until portfd is taken out of alert mode,
-		// all calls to port_getn will return immediately.
-		if port_alert(portfd, _PORT_ALERT_UPDATE, _POLLHUP, uintptr(unsafe.Pointer(&portfd))) < 0 {
-			if e := errno(); e != _EBUSY {
-				println("runtime: port_alert failed with", e)
-				throw("runtime: netpoll: port_alert failed")
-			}
+	// Failing to cas indicates there is an in-flight wakeup, so we're done here.
+	if !atomic.Cas(&netpollWakeSig, 0, 1) {
+		return
+	}
+
+	// Use port_alert to put portfd into alert mode.
+	// This will wake up all threads sleeping in port_getn on portfd,
+	// and cause their calls to port_getn to return immediately.
+	// Further, until portfd is taken out of alert mode,
+	// all calls to port_getn will return immediately.
+	if port_alert(portfd, _PORT_ALERT_UPDATE, _POLLHUP, uintptr(unsafe.Pointer(&portfd))) < 0 {
+		if e := errno(); e != _EBUSY {
+			println("runtime: port_alert failed with", e)
+			throw("runtime: netpoll: port_alert failed")
 		}
 	}
 }
diff --git a/src/runtime/netpoll_windows.go b/src/runtime/netpoll_windows.go
index 4c1cd2633a8..7e4664909cc 100644
--- a/src/runtime/netpoll_windows.go
+++ b/src/runtime/netpoll_windows.go
@@ -67,11 +67,14 @@ func netpollarm(pd *pollDesc, mode int) {
 }
 
 func netpollBreak() {
-	if atomic.Cas(&netpollWakeSig, 0, 1) {
-		if stdcall4(_PostQueuedCompletionStatus, iocphandle, 0, 0, 0) == 0 {
-			println("runtime: netpoll: PostQueuedCompletionStatus failed (errno=", getlasterror(), ")")
-			throw("runtime: netpoll: PostQueuedCompletionStatus failed")
-		}
+	// Failing to cas indicates there is an in-flight wakeup, so we're done here.
+	if !atomic.Cas(&netpollWakeSig, 0, 1) {
+		return
+	}
+
+	if stdcall4(_PostQueuedCompletionStatus, iocphandle, 0, 0, 0) == 0 {
+		println("runtime: netpoll: PostQueuedCompletionStatus failed (errno=", getlasterror(), ")")
+		throw("runtime: netpoll: PostQueuedCompletionStatus failed")
 	}
 }