diff --git a/pom.xml b/pom.xml
index 1b5b052..abc5712 100644
--- a/pom.xml
+++ b/pom.xml
@@ -34,7 +34,21 @@
         <dependency>
             <groupId>com.squareup.okhttp3</groupId>
             <artifactId>okhttp</artifactId>
-            <version>3.2.0</version>
+            <version>4.8.1</version>
+        </dependency>
+
+        <dependency>
+            <groupId>com.squareup.okhttp3</groupId>
+            <artifactId>mockwebserver</artifactId>
+            <version>4.8.1</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>com.squareup.okhttp3</groupId>
+            <artifactId>okhttp-tls</artifactId>
+            <version>4.8.1</version>
+            <scope>test</scope>
         </dependency>
 
         <dependency>
diff --git a/src/main/java/com/clevertap/apns/clients/SyncOkHttpApnsClient.java b/src/main/java/com/clevertap/apns/clients/SyncOkHttpApnsClient.java
index 86e8c22..edde700 100644
--- a/src/main/java/com/clevertap/apns/clients/SyncOkHttpApnsClient.java
+++ b/src/main/java/com/clevertap/apns/clients/SyncOkHttpApnsClient.java
@@ -43,6 +43,7 @@
 import java.security.cert.CertificateException;
 import java.security.cert.X509Certificate;
 import java.security.spec.InvalidKeySpecException;
+import java.util.Arrays;
 import java.util.UUID;
 
 /**
@@ -178,11 +179,19 @@ public SyncOkHttpApnsClient(InputStream certificate, String password, boolean pr
 
         final TrustManagerFactory tmf = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
         tmf.init((KeyStore) null);
-        sslContext.init(keyManagers, tmf.getTrustManagers(), null);
+
+            // check if there is an existing TrustManager configured in the builder
+        TrustManager[] trustManagers = (builder.getX509TrustManagerOrNull$okhttp() != null) ?
+            new TrustManager[] {builder.getX509TrustManagerOrNull$okhttp()} : tmf.getTrustManagers();
+        sslContext.init(keyManagers, trustManagers, null);
+
+        if (trustManagers.length != 1 || !(trustManagers[0] instanceof X509TrustManager)) {
+            throw new IllegalStateException("Unexpected default trust managers:" + Arrays.toString(trustManagers));
+        }
 
         final SSLSocketFactory sslSocketFactory = sslContext.getSocketFactory();
 
-        builder.sslSocketFactory(sslSocketFactory);
+        builder.sslSocketFactory(sslSocketFactory, (X509TrustManager) trustManagers[0]);
 
         client = builder.build();
 
diff --git a/src/test/java/com/clevertap/apns/LocalHttpServer.java b/src/test/java/com/clevertap/apns/LocalHttpServer.java
new file mode 100644
index 0000000..32855ec
--- /dev/null
+++ b/src/test/java/com/clevertap/apns/LocalHttpServer.java
@@ -0,0 +1,66 @@
+package com.clevertap.apns;
+
+import com.sun.net.httpserver.HttpExchange;
+import com.sun.net.httpserver.HttpHandler;
+import com.sun.net.httpserver.HttpServer;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.net.InetSocketAddress;
+import java.net.ServerSocket;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+public class LocalHttpServer {
+
+    private final ExecutorService executorService = Executors.newFixedThreadPool(10);
+    HttpServer httpServer;
+    int port;
+    String LOCAL_HOST = "http://127.0.0.1";
+    String CONTEXT = "/serveRequest";
+
+    public static int nextFreePort() {
+        try {
+            try (ServerSocket tempSocket = new ServerSocket(0)) {
+                return tempSocket.getLocalPort();
+            }
+        } catch (IOException e) {
+            return -1;
+        }
+    }
+
+    public int init() throws Exception {
+        port = nextFreePort();
+        baseConfig(port);
+        return port;
+    }
+
+    public String getUrl() {
+        return LOCAL_HOST + ":" + port + CONTEXT;
+    }
+
+    public void baseConfig(int port) throws Exception {
+        httpServer = HttpServer.create(new InetSocketAddress(port), 0);
+        httpServer.createContext(CONTEXT, new RequestHandler());
+        httpServer.setExecutor(executorService); // creates a default executor
+        httpServer.start();
+        System.out.println("Local Http server created on port " + port);
+    }
+
+    public void shutDownServer() {
+        httpServer.stop(1);
+        executorService.shutdown();
+    }
+
+    static class RequestHandler implements HttpHandler {
+        @Override
+        public void handle(HttpExchange t) throws IOException {
+            String response = "Request Executed";
+            t.getResponseHeaders().set("Content-Type", "text/plain");
+            t.sendResponseHeaders(200, response.length());
+            OutputStream os = t.getResponseBody();
+            os.write(response.getBytes());
+            os.close();
+        }
+    }
+}
diff --git a/src/test/java/com/clevertap/apns/clients/SyncOkHttpApnsClientTest.java b/src/test/java/com/clevertap/apns/clients/SyncOkHttpApnsClientTest.java
new file mode 100644
index 0000000..a8c0b79
--- /dev/null
+++ b/src/test/java/com/clevertap/apns/clients/SyncOkHttpApnsClientTest.java
@@ -0,0 +1,202 @@
+package com.clevertap.apns.clients;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+import java.security.KeyStore;
+import java.security.cert.Certificate;
+import java.security.cert.X509Certificate;
+
+import com.clevertap.apns.ApnsClient;
+import com.clevertap.apns.LocalHttpServer;
+import com.clevertap.apns.Notification;
+import com.clevertap.apns.NotificationResponse;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import okhttp3.HttpUrl;
+import okhttp3.OkHttpClient;
+import okhttp3.mockwebserver.MockResponse;
+import okhttp3.mockwebserver.MockWebServer;
+import okhttp3.mockwebserver.RecordedRequest;
+import okhttp3.tls.HandshakeCertificates;
+import okhttp3.tls.HeldCertificate;
+
+
+public class SyncOkHttpApnsClientTest {
+
+    protected static final String DEFAULT_TOPIC = "com.clevertap.testTopic";
+    protected static final String CERT_PASSWD = "cert-password";
+    protected static final String DEVICE_TOKEN = "vaild-device-token";
+    protected static final String INVALID_DEVICE_TOKEN = "invaild-device-token";
+
+    protected HeldCertificate rootCertificate;
+    protected HeldCertificate serverCertificate;
+    protected HeldCertificate clientCertificate;
+    protected HandshakeCertificates serverCertificateChain;
+    protected HandshakeCertificates clientCertificateChain;
+
+    @Before
+    public void initCertificates() {
+        rootCertificate = new HeldCertificate.Builder()
+            .certificateAuthority(0)
+            .build();
+
+        serverCertificate = new HeldCertificate.Builder()
+            .addSubjectAlternativeName("localhost")
+            .commonName("localhost")
+            .signedBy(rootCertificate)
+            .build();
+
+        clientCertificate = new HeldCertificate.Builder()
+            .commonName("push")
+            .signedBy(rootCertificate)
+            .build();
+
+        serverCertificateChain = new HandshakeCertificates.Builder()
+            .heldCertificate(serverCertificate)
+            .addTrustedCertificate(rootCertificate.certificate())
+            .build();
+
+            // Don't add client cert to client cert chain b/c it will be added via the apns api
+        clientCertificateChain = new HandshakeCertificates.Builder()
+            .addTrustedCertificate(rootCertificate.certificate())
+            .build();
+    }
+
+    /**
+     * Convert client cert to PKCS12 Format and return as InputStream.
+     * @return
+     */
+    protected InputStream getClientCertPKCS12() {
+        try {
+            KeyStore pkcs12 = KeyStore.getInstance("PKCS12");
+            pkcs12.load(null, null);
+            Certificate chain[] = {clientCertificate.certificate()};
+            pkcs12.setKeyEntry("privatekeyalias", clientCertificate.keyPair().getPrivate(), CERT_PASSWD.toCharArray(), chain);
+            
+            ByteArrayOutputStream outStream = new ByteArrayOutputStream();
+            pkcs12.store(outStream, CERT_PASSWD.toCharArray());
+
+            return new ByteArrayInputStream(outStream.toByteArray());
+        } catch(Exception e) {
+            fail(e.getMessage());
+        }
+        return null;
+    }
+
+    /**
+     * Changes Gateway-URL of the ApnsClient instance to the given URL via reflection.
+     * 
+     * @param client  ApnsClient instance which gatewayUrl shall be changed
+     * @param gatewayUrl  URL to set
+     */
+    protected void setClientGatewayUrl(ApnsClient client, HttpUrl gatewayUrl) {
+        try {
+            String url = gatewayUrl.toString();
+
+                // strip trailling slash
+            if (url.endsWith("/")) {
+                url = url.substring(0, url.length() - 1);
+            }
+
+            Field field = client.getClass().getDeclaredField("gateway");
+            field.setAccessible(true);
+
+            Field modifiers = Field.class.getDeclaredField("modifiers");
+            modifiers.setAccessible(true);
+            modifiers.setInt(field, field.getModifiers() & ~Modifier.FINAL);
+
+            field.set(client, url);
+        } catch (Exception e) {
+            fail(e.getMessage());
+        }
+    }
+
+    /**
+     * Build ApnsClient with valid client cert in synchronous mode.
+     * @return apnsClient
+     */
+    private ApnsClient buildClientWithCert() {
+        try {
+            return new ApnsClientBuilder()
+                .withOkHttpClientBuilder(new OkHttpClient.Builder().sslSocketFactory(clientCertificateChain.sslSocketFactory(), clientCertificateChain.trustManager()))
+                .withDefaultTopic(DEFAULT_TOPIC)
+                .withCertificate(getClientCertPKCS12())
+                .withPassword(CERT_PASSWD)
+                .inSynchronousMode()
+                .withProductionGateway()
+                .build();
+        } catch (Exception e) {
+            fail(e.getMessage());
+        }
+        return null;
+    }
+
+    @Test
+    public void pushTestWithCert() {
+        MockWebServer server = new MockWebServer();
+        try {
+            server.useHttps(serverCertificateChain.sslSocketFactory(), false);
+            server.requestClientAuth();
+            server.enqueue(new MockResponse().setResponseCode(200).setBody("Hello world!"));
+            
+            ApnsClient client = buildClientWithCert();
+            setClientGatewayUrl(client, server.url(""));
+
+            NotificationResponse response = client.push(
+                new Notification.Builder(DEVICE_TOKEN)
+                    .alertBody("Notification Body")
+                    .alertTitle("Alert Title")
+                    .badge(10)
+                    .sound("sound")
+                    .build()
+            );
+            assertEquals("HTTP-Response-Code 200", 200, response.getHttpStatusCode());
+            
+            RecordedRequest request = server.takeRequest();
+            assertEquals("/3/device/" + DEVICE_TOKEN, request.getPath());
+            assertEquals(DEFAULT_TOPIC, request.getHeader("apns-topic"));
+
+            X509Certificate clientCert = (X509Certificate) request.getHandshake().peerCertificates().get(0);
+            X509Certificate clientChain[] = {clientCert};
+            serverCertificateChain.trustManager().checkClientTrusted(clientChain, "RSA");
+
+        } catch (Exception e) {
+            fail(e.getMessage());
+        }
+
+        try {
+            server.close();
+        } catch (IOException e) {
+            fail(e.getMessage());
+        }
+    }
+
+    @Test
+    public void pushTestWithCertificateWithLocalHttpServer() throws Exception {
+        LocalHttpServer localHttpServer = new LocalHttpServer();
+        localHttpServer.init();
+        HttpUrl url = HttpUrl.parse(localHttpServer.getUrl());
+        ApnsClient client = buildClientWithCert();
+        setClientGatewayUrl(client, url);
+
+        NotificationResponse response = client.push(
+                new Notification.Builder(DEVICE_TOKEN)
+                        .alertBody("Notification Body")
+                        .alertTitle("Alert Title")
+                        .badge(10)
+                        .sound("sound")
+                        .build()
+        );
+        assertEquals("Server should be hit and should return 200", 200, response.getHttpStatusCode());
+        localHttpServer.shutDownServer();
+    }
+}
\ No newline at end of file