diff --git a/src/cmd/go/testdata/script/testing_issue40908.txt b/src/cmd/go/testdata/script/testing_issue40908.txt
new file mode 100644
index 0000000..4939de0
--- /dev/null
+++ b/src/cmd/go/testdata/script/testing_issue40908.txt
@@ -0,0 +1,21 @@
+[short] skip
+[!race] skip
+
+go test -race testrace
+
+-- testrace/race_test.go --
+package testrace
+
+import "testing"
+
+func TestRace(t *testing.T) {
+	helperDone := make(chan struct{})
+	go func() {
+		t.Logf("Something happened before cleanup.")
+		close(helperDone)
+	}()
+
+	t.Cleanup(func() {
+		<-helperDone
+	})
+}
diff --git a/src/testing/testing.go b/src/testing/testing.go
index 6fc8c4f..bf83df8 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -860,11 +860,15 @@
 	c.cleanup = func() {
 		if oldCleanup != nil {
 			defer func() {
+				c.mu.Lock()
 				c.cleanupPc = oldCleanupPc
+				c.mu.Unlock()
 				oldCleanup()
 			}()
 		}
+		c.mu.Lock()
 		c.cleanupName = callerName(0)
+		c.mu.Unlock()
 		f()
 	}
 	var pc [maxStackLen]uintptr