src/net/http/serve_test.go | 10 ++++++++++
 src/net/http/server.go     |  3 +++

diff --git a/src/net/http/serve_test.go b/src/net/http/serve_test.go
index 9cbfe872afe0bc53522e32bf95879e4e72f03252..1df319ac1fc571956654ee11f96bccb320a96d43 100644
--- a/src/net/http/serve_test.go
+++ b/src/net/http/serve_test.go
@@ -581,6 +581,16 @@ 		}
 	}
 }
 
+func TestShouldRedirectConcurrency(t *testing.T) {
+	setParallel(t)
+	defer afterTest(t)
+
+	mux := NewServeMux()
+	ts := httptest.NewServer(mux)
+	defer ts.Close()
+	mux.HandleFunc("/", func(w ResponseWriter, r *Request) {})
+}
+
 func BenchmarkServeMux(b *testing.B) {
 
 	type test struct {
diff --git a/src/net/http/server.go b/src/net/http/server.go
index 57e1b5dacb3faf3dbecb5bbecba6d242580164d5..88e00a2eddc62efc7c83ec977e22eac98763cdf7 100644
--- a/src/net/http/server.go
+++ b/src/net/http/server.go
@@ -2233,6 +2233,9 @@ // shouldRedirect reports whether the given path and host should be redirected to
 // path+"/". This should happen if a handler is registered for path+"/" but
 // not path -- see comments at ServeMux.
 func (mux *ServeMux) shouldRedirect(host, path string) bool {
+	mux.mu.RLock()
+	defer mux.mu.RUnlock()
+
 	p := []string{path, host + path}
 
 	for _, c := range p {