diff --git a/src/testing/testing.go b/src/testing/testing.go
index d546f56478..44bccd384e 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -806,7 +806,12 @@ func (c *common) Cleanup(f func()) {
 func (c *common) TempDir() string {
 	c.tempDirOnce.Do(func() {
 		c.Helper()
-		c.tempDir, c.tempDirErr = ioutil.TempDir("", c.Name())
+
+		// ioutil.TempDir doesn't like path separators in its pattern,
+		// so mangle the name to accommodate subtests.
+		pattern := strings.ReplaceAll(c.Name(), "/", "_")
+
+		c.tempDir, c.tempDirErr = ioutil.TempDir("", pattern)
 		if c.tempDirErr == nil {
 			c.Cleanup(func() {
 				if err := os.RemoveAll(c.tempDir); err != nil {
diff --git a/src/testing/testing_test.go b/src/testing/testing_test.go
index afb35a96d4..07757a8482 100644
--- a/src/testing/testing_test.go
+++ b/src/testing/testing_test.go
@@ -19,6 +19,11 @@ func TestMain(m *testing.M) {
 }
 
 func TestTempDir(t *testing.T) {
+	testTempDir(t)
+	t.Run("InSubtest", testTempDir)
+}
+
+func testTempDir(t *testing.T) {
 	dirCh := make(chan string, 1)
 	t.Cleanup(func() {
 		// Verify directory has been removed.