diff --git a/misc/cgo/test/cgo_test.go b/misc/cgo/test/cgo_test.go
index ccacc50fe1a..ae856a37d69 100644
--- a/misc/cgo/test/cgo_test.go
+++ b/misc/cgo/test/cgo_test.go
@@ -92,6 +92,7 @@ func Test25143(t *testing.T)                 { test25143(t) }
 func Test23356(t *testing.T)                 { test23356(t) }
 func Test26066(t *testing.T)                 { test26066(t) }
 func Test26213(t *testing.T)                 { test26213(t) }
+func Test27660(t *testing.T)                 { test27660(t) }
 
 func BenchmarkCgoCall(b *testing.B)  { benchCgoCall(b) }
 func BenchmarkGoString(b *testing.B) { benchGoString(b) }
diff --git a/misc/cgo/test/test27660.go b/misc/cgo/test/test27660.go
new file mode 100644
index 00000000000..8c23b7dc58f
--- /dev/null
+++ b/misc/cgo/test/test27660.go
@@ -0,0 +1,54 @@
+// Copyright 2018 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.
+
+// Stress the interaction between the race detector and cgo in an
+// attempt to reproduce the memory corruption described in #27660.
+// The bug was very timing sensitive; at the time of writing this
+// test would only trigger the bug about once out of every five runs.
+
+package cgotest
+
+// #include <unistd.h>
+import "C"
+
+import (
+	"context"
+	"math/rand"
+	"runtime"
+	"sync"
+	"testing"
+	"time"
+)
+
+func test27660(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	ints := make([]int, 100)
+	locks := make([]sync.Mutex, 100)
+	// Slowly create threads so that ThreadSanitizer is forced to
+	// frequently resize its SyncClocks.
+	for i := 0; i < 100; i++ {
+		go func() {
+			for ctx.Err() == nil {
+				// Sleep in C for long enough that it is likely that the runtime
+				// will retake this goroutine's currently wired P.
+				C.usleep(1000 /* 1ms */)
+				runtime.Gosched() // avoid starvation (see #28701)
+			}
+		}()
+		go func() {
+			// Trigger lots of synchronization and memory reads/writes to
+			// increase the likelihood that the race described in #27660
+			// results in corruption of ThreadSanitizer's internal state
+			// and thus an assertion failure or segfault.
+			for ctx.Err() == nil {
+				j := rand.Intn(100)
+				locks[j].Lock()
+				ints[j]++
+				locks[j].Unlock()
+			}
+		}()
+		time.Sleep(time.Millisecond)
+	}
+}
diff --git a/src/runtime/cgocall.go b/src/runtime/cgocall.go
index 86bd2fb01c0..ca31408b507 100644
--- a/src/runtime/cgocall.go
+++ b/src/runtime/cgocall.go
@@ -130,12 +130,19 @@ func cgocall(fn, arg unsafe.Pointer) int32 {
 	mp.incgo = true
 	errno := asmcgocall(fn, arg)
 
-	// Call endcgo before exitsyscall because exitsyscall may
+	// Update accounting before exitsyscall because exitsyscall may
 	// reschedule us on to a different M.
-	endcgo(mp)
+	mp.incgo = false
+	mp.ncgo--
 
 	exitsyscall()
 
+	// Note that raceacquire must be called only after exitsyscall has
+	// wired this M to a P.
+	if raceenabled {
+		raceacquire(unsafe.Pointer(&racecgosync))
+	}
+
 	// From the garbage collector's perspective, time can move
 	// backwards in the sequence above. If there's a callback into
 	// Go code, GC will see this function at the call to
@@ -153,16 +160,6 @@ func cgocall(fn, arg unsafe.Pointer) int32 {
 	return errno
 }
 
-//go:nosplit
-func endcgo(mp *m) {
-	mp.incgo = false
-	mp.ncgo--
-
-	if raceenabled {
-		raceacquire(unsafe.Pointer(&racecgosync))
-	}
-}
-
 // Call from C back to Go.
 //go:nosplit
 func cgocallbackg(ctxt uintptr) {
@@ -347,13 +344,14 @@ func unwindm(restore *bool) {
 			sched.sp = *(*uintptr)(unsafe.Pointer(sched.sp + 16))
 		}
 
-		// Call endcgo to do the accounting that cgocall will not have a
-		// chance to do during an unwind.
+		// Do the accounting that cgocall will not have a chance to do
+		// during an unwind.
 		//
 		// In the case where a Go call originates from C, ncgo is 0
 		// and there is no matching cgocall to end.
 		if mp.ncgo > 0 {
-			endcgo(mp)
+			mp.incgo = false
+			mp.ncgo--
 		}
 
 		releasem(mp)