diff --git a/.gitignore b/.gitignore
index 35531439..9f72feeb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
 /.tmp/
 *.pprof
 *.svg
+.idea
 cover.out
 connect.test
diff --git a/internal/memhttp/memhttp.go b/internal/memhttp/memhttp.go
index f8046426..49fc3328 100644
--- a/internal/memhttp/memhttp.go
+++ b/internal/memhttp/memhttp.go
@@ -33,6 +33,11 @@ type Server struct {
 
 	serverWG  sync.WaitGroup
 	serverErr error
+
+	// client is configured for use with the server.
+	// Its transport is automatically closed when Close is called.
+	client   *http.Client
+	clientMu sync.Mutex
 }
 
 // NewServer creates a new Server that uses the given handler. Configuration
@@ -94,12 +99,18 @@ func (s *Server) TransportHTTP1() *http.Transport {
 }
 
 // Client returns an [http.Client] configured to use in-memory pipes rather
-// than TCP and speak HTTP/2. It is configured to use the same
-// [http2.Transport] as [Transport].
+// than TCP and speak HTTP/2.
 //
-// Callers may reconfigure the returned client without affecting other clients.
+// Client is configured to use the same transport for the lifetime of the
+// server, and its idle connections are automatically closed when the
+// server is closed.
 func (s *Server) Client() *http.Client {
-	return &http.Client{Transport: s.Transport()}
+	s.clientMu.Lock()
+	defer s.clientMu.Unlock()
+	if s.client == nil {
+		s.client = &http.Client{Transport: s.Transport()}
+	}
+	return s.client
 }
 
 // URL returns the server's URL.
@@ -110,6 +121,11 @@ func (s *Server) URL() string {
 // Shutdown gracefully shuts down the server, without interrupting any active
 // connections. See [http.Server.Shutdown] for details.
 func (s *Server) Shutdown(ctx context.Context) error {
+	s.clientMu.Lock()
+	if s.client != nil {
+		s.client.CloseIdleConnections()
+	}
+	s.clientMu.Unlock()
 	if err := s.server.Shutdown(ctx); err != nil {
 		return err
 	}
@@ -128,6 +144,11 @@ func (s *Server) Cleanup() error {
 // Close closes the server's listener. It does not wait for connections to
 // finish.
 func (s *Server) Close() error {
+	s.clientMu.Lock()
+	if s.client != nil {
+		s.client.CloseIdleConnections()
+	}
+	s.clientMu.Unlock()
 	return s.server.Close()
 }
 
diff --git a/internal/memhttp/memhttptest/http_test.go b/internal/memhttp/memhttptest/http_test.go
new file mode 100644
index 00000000..8f62422a
--- /dev/null
+++ b/internal/memhttp/memhttptest/http_test.go
@@ -0,0 +1,112 @@
+// Copyright 2021-2025 The Connect Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build go1.25
+
+// Copyright 2021-2025 The Connect Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package memhttptest_test
+
+import (
+	"bytes"
+	"io"
+	"net/http"
+	"strings"
+	"testing"
+	"testing/synctest"
+
+	"connectrpc.com/connect/internal/assert"
+	"connectrpc.com/connect/internal/memhttp"
+	"connectrpc.com/connect/internal/memhttp/memhttptest"
+)
+
+// TestMemhttpWithSynctest verifies that memhttp works correctly with synctest.
+func TestMemhttpWithSynctest(t *testing.T) {
+	t.Parallel()
+	body := "request body"
+
+	handler := http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
+		buf := &bytes.Buffer{}
+		_, err := io.Copy(buf, request.Body)
+		if err != nil {
+			t.Errorf("failed to copy body: %v", err)
+		}
+		if buf.String() != body {
+			t.Errorf("got body %q, want %q", buf.String(), body)
+		}
+		writer.WriteHeader(http.StatusOK)
+	})
+
+	tests := []struct {
+		name   string
+		client func(*testing.T, *memhttp.Server) *http.Client
+	}{
+		{
+			name: "server.Client()",
+			client: func(t *testing.T, s *memhttp.Server) *http.Client {
+				t.Helper()
+				return s.Client()
+			},
+		},
+		{
+			name: "Custom Client HTTP/1",
+			client: func(t *testing.T, s *memhttp.Server) *http.Client {
+				t.Helper()
+				// HTTP/1.1's is a per-request closure, so nothing leaks outside the bubble.
+				return &http.Client{Transport: s.TransportHTTP1()}
+			},
+		},
+		{
+			name: "Custom Client HTTP/2",
+			client: func(t *testing.T, s *memhttp.Server) *http.Client {
+				t.Helper()
+				// HTTP/2 a goroutine running for future connections, which leaks outside the bubble.
+				client := &http.Client{Transport: s.Transport()}
+				// Closing idle connections here ensures synctest doesn't panic.
+				t.Cleanup(client.CloseIdleConnections)
+				return client
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			synctest.Test(t, func(t *testing.T) {
+				t.Helper()
+				server := memhttptest.NewServer(t, handler)
+
+				req, err := http.NewRequestWithContext(t.Context(), http.MethodPut, server.URL(), strings.NewReader(body))
+				assert.Nil(t, err)
+
+				client := test.client(t, server)
+				resp, err := client.Do(req)
+				assert.Nil(t, err)
+				resp.Body.Close()
+			})
+		})
+	}
+}