diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index fc77a964b6..bdf73e0412 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -2703,7 +2703,6 @@ func goexit0(gp *g) {
 		print("invalid m->lockedInt = ", _g_.m.lockedInt, "\n")
 		throw("internal lockOSThread error")
 	}
-	_g_.m.lockedExt = 0
 	gfput(_g_.m.p.ptr(), gp)
 	if locked {
 		// The goroutine may have locked this thread because
@@ -2714,6 +2713,10 @@ func goexit0(gp *g) {
 		// the thread.
 		if GOOS != "plan9" { // See golang.org/issue/22227.
 			gogo(&_g_.m.g0.sched)
+		} else {
+			// Clear lockedExt on plan9 since we may end up re-using
+			// this thread.
+			_g_.m.lockedExt = 0
 		}
 	}
 	schedule()
diff --git a/src/runtime/proc_test.go b/src/runtime/proc_test.go
index ad325987ac..e6947d5849 100644
--- a/src/runtime/proc_test.go
+++ b/src/runtime/proc_test.go
@@ -885,6 +885,12 @@ func TestLockOSThreadNesting(t *testing.T) {
 
 func TestLockOSThreadExit(t *testing.T) {
 	testLockOSThreadExit(t, "testprog")
+
+	want := "OK\n"
+	output := runTestProg(t, "testprog", "LockOSThreadAvoidsStatePropagation", "GOMAXPROCS=1")
+	if output != want {
+		t.Errorf("want %s, got %s\n", want, output)
+	}
 }
 
 func testLockOSThreadExit(t *testing.T, prog string) {
diff --git a/src/runtime/testdata/testprog/gettid.go b/src/runtime/testdata/testprog/gettid.go
deleted file mode 100644
index 1b3e29ab08..0000000000
--- a/src/runtime/testdata/testprog/gettid.go
+++ /dev/null
@@ -1,29 +0,0 @@
-// Copyright 2017 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build linux
-
-package main
-
-import (
-	"bytes"
-	"fmt"
-	"io/ioutil"
-	"os"
-	"syscall"
-)
-
-func gettid() int {
-	return syscall.Gettid()
-}
-
-func tidExists(tid int) (exists, supported bool) {
-	stat, err := ioutil.ReadFile(fmt.Sprintf("/proc/self/task/%d/stat", tid))
-	if os.IsNotExist(err) {
-		return false, true
-	}
-	// Check if it's a zombie thread.
-	state := bytes.Fields(stat)[2]
-	return !(len(state) == 1 && state[0] == 'Z'), true
-}
diff --git a/src/runtime/testdata/testprog/lockosthread.go b/src/runtime/testdata/testprog/lockosthread.go
index 88c0d12e4c..5119cf8131 100644
--- a/src/runtime/testdata/testprog/lockosthread.go
+++ b/src/runtime/testdata/testprog/lockosthread.go
@@ -24,6 +24,12 @@ func init() {
 		runtime.LockOSThread()
 	})
 	register("LockOSThreadAlt", LockOSThreadAlt)
+
+	registerInit("LockOSThreadAvoidsStatePropagation", func() {
+		// Lock the OS thread now so main runs on the main thread.
+		runtime.LockOSThread()
+	})
+	register("LockOSThreadAvoidsStatePropagation", LockOSThreadAvoidsStatePropagation)
 }
 
 func LockOSThreadMain() {
@@ -92,3 +98,96 @@ func LockOSThreadAlt() {
 ok:
 	println("OK")
 }
+
+func LockOSThreadAvoidsStatePropagation() {
+	// This test is similar to LockOSThreadAlt in that it will detect if a thread
+	// which should have died is still running. However, rather than do this with
+	// thread IDs, it does this by unsharing state on that thread. This way, it
+	// also detects whether new threads were cloned from the dead thread, and not
+	// from a clean thread. Cloning from a locked thread is undesirable since
+	// cloned threads will inherit potentially unwanted OS state.
+	//
+	// unshareFs, getcwd, and chdir("/tmp") are only guaranteed to work on
+	// Linux, so on other platforms this just checks that the runtime doesn't
+	// do anything terrible.
+	//
+	// This is running locked to the main OS thread.
+
+	// GOMAXPROCS=1 makes this fail much more reliably if a tainted thread is
+	// cloned from.
+	if runtime.GOMAXPROCS(-1) != 1 {
+		println("requires GOMAXPROCS=1")
+		os.Exit(1)
+	}
+
+	if err := chdir("/"); err != nil {
+		println("failed to chdir:", err.Error())
+		os.Exit(1)
+	}
+	// On systems other than Linux, cwd == "".
+	cwd, err := getcwd()
+	if err != nil {
+		println("failed to get cwd:", err.Error())
+		os.Exit(1)
+	}
+	if cwd != "" && cwd != "/" {
+		println("unexpected cwd", cwd, " wanted /")
+		os.Exit(1)
+	}
+
+	ready := make(chan bool, 1)
+	go func() {
+		// This goroutine must be running on a new thread.
+		runtime.LockOSThread()
+
+		// Unshare details about the FS, like the CWD, with
+		// the rest of the process on this thread.
+		// On systems other than Linux, this is a no-op.
+		if err := unshareFs(); err != nil {
+			println("failed to unshare fs:", err.Error())
+			os.Exit(1)
+		}
+		// Chdir to somewhere else on this thread.
+		// On systems other than Linux, this is a no-op.
+		if err := chdir("/tmp"); err != nil {
+			println("failed to chdir:", err.Error())
+			os.Exit(1)
+		}
+
+		// The state on this thread is now considered "tainted", but it
+		// should no longer be observable in any other context.
+
+		ready <- true
+		// Exit with the thread locked.
+	}()
+	<-ready
+
+	// Spawn yet another goroutine and lock it. Since GOMAXPROCS=1, if
+	// for some reason state from the (hopefully dead) locked thread above
+	// propagated into a newly created thread (via clone), or that thread
+	// is actually being re-used, then we should get scheduled on such a
+	// thread with high likelihood.
+	done := make(chan bool)
+	go func() {
+		runtime.LockOSThread()
+
+		// Get the CWD and check if this is the same as the main thread's
+		// CWD. Every thread should share the same CWD.
+		// On systems other than Linux, wd == "".
+		wd, err := getcwd()
+		if err != nil {
+			println("failed to get cwd:", err.Error())
+			os.Exit(1)
+		}
+		if wd != cwd {
+			println("bad state from old thread propagated after it should have died")
+			os.Exit(1)
+		}
+		<-done
+
+		runtime.UnlockOSThread()
+	}()
+	done <- true
+	runtime.UnlockOSThread()
+	println("OK")
+}
diff --git a/src/runtime/testdata/testprog/syscalls.go b/src/runtime/testdata/testprog/syscalls.go
new file mode 100644
index 0000000000..08284fc561
--- /dev/null
+++ b/src/runtime/testdata/testprog/syscalls.go
@@ -0,0 +1,54 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build linux
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"syscall"
+)
+
+func gettid() int {
+	return syscall.Gettid()
+}
+
+func tidExists(tid int) (exists, supported bool) {
+	stat, err := ioutil.ReadFile(fmt.Sprintf("/proc/self/task/%d/stat", tid))
+	if os.IsNotExist(err) {
+		return false, true
+	}
+	// Check if it's a zombie thread.
+	state := bytes.Fields(stat)[2]
+	return !(len(state) == 1 && state[0] == 'Z'), true
+}
+
+func getcwd() (string, error) {
+	if !syscall.ImplementsGetwd {
+		return "", nil
+	}
+	// Use the syscall to get the current working directory.
+	// This is imperative for checking for OS thread state
+	// after an unshare since os.Getwd might just check the
+	// environment, or use some other mechanism.
+	var buf [4096]byte
+	n, err := syscall.Getcwd(buf[:])
+	if err != nil {
+		return "", err
+	}
+	// Subtract one for null terminator.
+	return string(buf[:n-1]), nil
+}
+
+func unshareFs() error {
+	return syscall.Unshare(syscall.CLONE_FS)
+}
+
+func chdir(path string) error {
+	return syscall.Chdir(path)
+}
diff --git a/src/runtime/testdata/testprog/gettid_none.go b/src/runtime/testdata/testprog/syscalls_none.go
similarity index 68%
rename from src/runtime/testdata/testprog/gettid_none.go
rename to src/runtime/testdata/testprog/syscalls_none.go
index 036db87e10..7f8ded3994 100644
--- a/src/runtime/testdata/testprog/gettid_none.go
+++ b/src/runtime/testdata/testprog/syscalls_none.go
@@ -13,3 +13,15 @@ func gettid() int {
 func tidExists(tid int) (exists, supported bool) {
 	return false, false
 }
+
+func getcwd() (string, error) {
+	return "", nil
+}
+
+func unshareFs() error {
+	return nil
+}
+
+func chdir(path string) error {
+	return nil
+}