diff --git a/example/src/main/java/com/stripe/example/controller/AsyncTaskTokenController.kt b/example/src/main/java/com/stripe/example/controller/AsyncTaskTokenController.kt
index 00a12695ccd..6afb4fef8f0 100644
--- a/example/src/main/java/com/stripe/example/controller/AsyncTaskTokenController.kt
+++ b/example/src/main/java/com/stripe/example/controller/AsyncTaskTokenController.kt
@@ -45,7 +45,7 @@ class AsyncTaskTokenController(
         }
 
         progressDialogController.show(R.string.progressMessage)
-        stripe.createToken(cardToSave, tokenCallback)
+        stripe.createToken(cardToSave, callback = tokenCallback)
     }
 
     private class TokenCallbackImpl constructor(
diff --git a/stripe/src/main/java/com/stripe/android/ApiRequest.kt b/stripe/src/main/java/com/stripe/android/ApiRequest.kt
index fbad911f5f7..a50f21acda9 100644
--- a/stripe/src/main/java/com/stripe/android/ApiRequest.kt
+++ b/stripe/src/main/java/com/stripe/android/ApiRequest.kt
@@ -39,6 +39,10 @@ internal class ApiRequest internal constructor(
             options.stripeAccount?.let {
                 mapOf("Stripe-Account" to it)
             }.orEmpty()
+        ).plus(
+            options.idempotencyKey?.let {
+                mapOf("Idempotency-Key" to it)
+            }.orEmpty()
         ).plus(
             languageTag?.let { mapOf("Accept-Language" to it) }.orEmpty()
         )
@@ -67,7 +71,7 @@ internal class ApiRequest internal constructor(
 
     @Throws(UnsupportedEncodingException::class, InvalidRequestException::class)
     override fun getOutputBytes(): ByteArray {
-        return createQuery().toByteArray(charset(CHARSET))
+        return query.toByteArray(charset(CHARSET))
     }
 
     override fun toString(): String {
@@ -93,7 +97,8 @@ internal class ApiRequest internal constructor(
      */
     internal data class Options internal constructor(
         val apiKey: String,
-        val stripeAccount: String? = null
+        internal val stripeAccount: String? = null,
+        internal val idempotencyKey: String? = null
     ) {
         init {
             ApiKeyValidator().requireValid(apiKey)
diff --git a/stripe/src/main/java/com/stripe/android/Stripe.kt b/stripe/src/main/java/com/stripe/android/Stripe.kt
index 8388fbf3234..e9aaf7e278a 100644
--- a/stripe/src/main/java/com/stripe/android/Stripe.kt
+++ b/stripe/src/main/java/com/stripe/android/Stripe.kt
@@ -501,7 +501,7 @@ class Stripe internal constructor(
      * See [Retrieve a source](https://stripe.com/docs/api/sources/retrieve).
      *
      * @param sourceId the [Source.id] field of the desired Source object
-     * @param clientSecret the [Source.getClientSecret] field of the desired Source object
+     * @param clientSecret the [Source.clientSecret] field of the desired Source object
      * @return a [Source] if one could be found based on the input params, or `null` if
      * no such Source could be found.
      * @throws AuthenticationException failure to properly authenticate yourself (check your key)
@@ -530,11 +530,14 @@ class Stripe internal constructor(
      * See [Create an account token](https://stripe.com/docs/api/tokens/create_account).
      *
      * @param accountParams the [AccountParams] used to create this token
+     * @param idempotencyKey optional, see [Idempotent Requests](https://stripe.com/docs/api/idempotent_requests)
      * @param callback a [ApiResultCallback] to receive the result or error
      */
     @UiThread
+    @JvmOverloads
     fun createAccountToken(
         accountParams: AccountParams,
+        idempotencyKey: String? = null,
         callback: ApiResultCallback<Token>
     ) {
         val params = accountParams.toParamMap()
@@ -542,6 +545,7 @@ class Stripe internal constructor(
         createTokenFromParams(
             params,
             Token.TokenType.ACCOUNT,
+            idempotencyKey,
             callback
         )
     }
@@ -553,7 +557,10 @@ class Stripe internal constructor(
      * See [Create an account token](https://stripe.com/docs/api/tokens/create_account).
      *
      * @param accountParams params to use for this token.
+     * @param idempotencyKey optional, see [Idempotent Requests](https://stripe.com/docs/api/idempotent_requests)
+     *
      * @return a [Token] that can be used for this account.
+     *
      * @throws AuthenticationException failure to properly authenticate yourself (check your key)
      * @throws InvalidRequestException your request has invalid parameters
      * @throws APIConnectionException failure to connect to Stripe's API
@@ -563,11 +570,15 @@ class Stripe internal constructor(
     @Throws(AuthenticationException::class, InvalidRequestException::class,
         APIConnectionException::class, APIException::class)
     @WorkerThread
-    fun createAccountTokenSynchronous(accountParams: AccountParams): Token? {
+    @JvmOverloads
+    fun createAccountTokenSynchronous(
+        accountParams: AccountParams,
+        idempotencyKey: String? = null
+    ): Token? {
         return try {
             stripeRepository.createToken(
                 accountParams.toParamMap(),
-                ApiRequest.Options(publishableKey, stripeAccountId),
+                ApiRequest.Options(publishableKey, stripeAccountId, idempotencyKey),
                 Token.TokenType.ACCOUNT
             )
         } catch (exception: CardException) {
@@ -582,11 +593,14 @@ class Stripe internal constructor(
      * See [Create a bank account token](https://stripe.com/docs/api/tokens/create_bank_account).
      *
      * @param bankAccount the [BankAccount] used to create this token
+     * @param idempotencyKey optional, see [Idempotent Requests](https://stripe.com/docs/api/idempotent_requests)
      * @param callback a [ApiResultCallback] to receive the result or error
      */
     @UiThread
+    @JvmOverloads
     fun createBankAccountToken(
         bankAccount: BankAccount,
+        idempotencyKey: String? = null,
         callback: ApiResultCallback<Token>
     ) {
         val params = bankAccount.toParamMap()
@@ -594,6 +608,7 @@ class Stripe internal constructor(
         createTokenFromParams(
             params,
             Token.TokenType.BANK_ACCOUNT,
+            idempotencyKey,
             callback
         )
     }
@@ -605,7 +620,10 @@ class Stripe internal constructor(
      * See [Create a bank account token](https://stripe.com/docs/api/tokens/create_bank_account).
      *
      * @param bankAccount the [Card] to use for this token
+     * @param idempotencyKey optional, see [Idempotent Requests](https://stripe.com/docs/api/idempotent_requests)
+     *
      * @return a [Token] that can be used for this [BankAccount]
+     *
      * @throws AuthenticationException failure to properly authenticate yourself (check your key)
      * @throws InvalidRequestException your request has invalid parameters
      * @throws APIConnectionException failure to connect to Stripe's API
@@ -617,12 +635,16 @@ class Stripe internal constructor(
     @Throws(AuthenticationException::class, InvalidRequestException::class,
         APIConnectionException::class, CardException::class, APIException::class)
     @WorkerThread
-    fun createBankAccountTokenSynchronous(bankAccount: BankAccount): Token? {
+    @JvmOverloads
+    fun createBankAccountTokenSynchronous(
+        bankAccount: BankAccount,
+        idempotencyKey: String? = null
+    ): Token? {
         val params = bankAccount.toParamMap()
             .plus(stripeNetworkUtils.createUidParams())
         return stripeRepository.createToken(
             params,
-            ApiRequest.Options(publishableKey, stripeAccountId),
+            ApiRequest.Options(publishableKey, stripeAccountId, idempotencyKey),
             Token.TokenType.BANK_ACCOUNT
         )
     }
@@ -630,20 +652,23 @@ class Stripe internal constructor(
     /**
      * Create a PII token asynchronously.
      *
-     *
      * See [Create a PII account token](https://stripe.com/docs/api/tokens/create_pii).
      *
      * @param personalId the personal id used to create this token
+     * @param idempotencyKey optional, see [Idempotent Requests](https://stripe.com/docs/api/idempotent_requests)
      * @param callback a [ApiResultCallback] to receive the result or error
      */
     @UiThread
+    @JvmOverloads
     fun createPiiToken(
         personalId: String,
+        idempotencyKey: String? = null,
         callback: ApiResultCallback<Token>
     ) {
         createTokenFromParams(
             PiiTokenParams(personalId).toParamMap(),
             Token.TokenType.PII,
+            idempotencyKey,
             callback
         )
     }
@@ -655,7 +680,10 @@ class Stripe internal constructor(
      * See [Create a PII account token](https://stripe.com/docs/api/tokens/create_pii).
      *
      * @param personalId the personal ID to use for this token
+     * @param idempotencyKey optional, see [Idempotent Requests](https://stripe.com/docs/api/idempotent_requests)
+     *
      * @return a [Token] that can be used for this card
+     *
      * @throws AuthenticationException failure to properly authenticate yourself (check your key)
      * @throws InvalidRequestException your request has invalid parameters
      * @throws APIConnectionException failure to connect to Stripe's API
@@ -665,10 +693,14 @@ class Stripe internal constructor(
     @Throws(AuthenticationException::class, InvalidRequestException::class,
         APIConnectionException::class, CardException::class, APIException::class)
     @WorkerThread
-    fun createPiiTokenSynchronous(personalId: String): Token? {
+    @JvmOverloads
+    fun createPiiTokenSynchronous(
+        personalId: String,
+        idempotencyKey: String? = null
+    ): Token? {
         return stripeRepository.createToken(
             PiiTokenParams(personalId).toParamMap(),
-            ApiRequest.Options(publishableKey, stripeAccountId),
+            ApiRequest.Options(publishableKey, stripeAccountId, idempotencyKey),
             Token.TokenType.PII
         )
     }
@@ -679,13 +711,20 @@ class Stripe internal constructor(
      * See [Create a card token](https://stripe.com/docs/api/tokens/create_card).
      *
      * @param card the [Card] used to create this payment token
+     * @param idempotencyKey optional, see [Idempotent Requests](https://stripe.com/docs/api/idempotent_requests)
      * @param callback a [ApiResultCallback] to receive the result or error
      */
     @UiThread
-    fun createToken(card: Card, callback: ApiResultCallback<Token>) {
+    @JvmOverloads
+    fun createToken(
+        card: Card,
+        idempotencyKey: String? = null,
+        callback: ApiResultCallback<Token>
+    ) {
         createTokenFromParams(
             stripeNetworkUtils.createCardTokenParams(card),
             Token.TokenType.CARD,
+            idempotencyKey,
             callback
         )
     }
@@ -697,6 +736,8 @@ class Stripe internal constructor(
      * See [Create a card token](https://stripe.com/docs/api/tokens/create_card).
      *
      * @param card the [Card] to use for this token
+     * @param idempotencyKey optional, see [Idempotent Requests](https://stripe.com/docs/api/idempotent_requests)
+     *
      * @return a [Token] that can be used for this card
      * @throws AuthenticationException failure to properly authenticate yourself (check your key)
      * @throws InvalidRequestException your request has invalid parameters
@@ -708,10 +749,14 @@ class Stripe internal constructor(
     @Throws(AuthenticationException::class, InvalidRequestException::class,
         APIConnectionException::class, CardException::class, APIException::class)
     @WorkerThread
-    fun createCardTokenSynchronous(card: Card): Token? {
+    @JvmOverloads
+    fun createCardTokenSynchronous(
+        card: Card,
+        idempotencyKey: String? = null
+    ): Token? {
         return stripeRepository.createToken(
             stripeNetworkUtils.createCardTokenParams(card),
-            ApiRequest.Options(publishableKey, stripeAccountId),
+            ApiRequest.Options(publishableKey, stripeAccountId, idempotencyKey),
             Token.TokenType.CARD
         )
     }
@@ -720,16 +765,20 @@ class Stripe internal constructor(
      * Create a CVC update token asynchronously.
      *
      * @param cvc the CVC used to create this token
+     * @param idempotencyKey optional, see [Idempotent Requests](https://stripe.com/docs/api/idempotent_requests)
      * @param callback a [ApiResultCallback] to receive the result or error
      */
     @UiThread
+    @JvmOverloads
     fun createCvcUpdateToken(
         @Size(min = 3, max = 4) cvc: String,
+        idempotencyKey: String? = null,
         callback: ApiResultCallback<Token>
     ) {
         createTokenFromParams(
             CvcTokenParams(cvc).toParamMap(),
             Token.TokenType.CVC_UPDATE,
+            idempotencyKey,
             callback
         )
     }
@@ -739,7 +788,10 @@ class Stripe internal constructor(
      * or your app will crash.
      *
      * @param cvc the CVC to use for this token
+     * @param idempotencyKey optional, see [Idempotent Requests](https://stripe.com/docs/api/idempotent_requests)
+     *
      * @return a [Token] that can be used for this card
+     *
      * @throws AuthenticationException failure to properly authenticate yourself (check your key)
      * @throws InvalidRequestException your request has invalid parameters
      * @throws APIConnectionException failure to connect to Stripe's API
@@ -749,10 +801,14 @@ class Stripe internal constructor(
     @Throws(AuthenticationException::class, InvalidRequestException::class,
         APIConnectionException::class, CardException::class, APIException::class)
     @WorkerThread
-    fun createCvcUpdateTokenSynchronous(cvc: String): Token? {
+    @JvmOverloads
+    fun createCvcUpdateTokenSynchronous(
+        cvc: String,
+        idempotencyKey: String? = null
+    ): Token? {
         return stripeRepository.createToken(
             CvcTokenParams(cvc).toParamMap(),
-            ApiRequest.Options(publishableKey, stripeAccountId),
+            ApiRequest.Options(publishableKey, stripeAccountId, idempotencyKey),
             Token.TokenType.CVC_UPDATE
         )
     }
@@ -760,11 +816,12 @@ class Stripe internal constructor(
     private fun createTokenFromParams(
         tokenParams: Map<String, Any>,
         @Token.TokenType tokenType: String,
+        idempotencyKey: String? = null,
         callback: ApiResultCallback<Token>
     ) {
         tokenCreator.create(
             tokenParams,
-            ApiRequest.Options(publishableKey, stripeAccountId),
+            ApiRequest.Options(publishableKey, stripeAccountId, idempotencyKey),
             tokenType, null,
             callback
         )
diff --git a/stripe/src/main/java/com/stripe/android/StripeRequest.kt b/stripe/src/main/java/com/stripe/android/StripeRequest.kt
index ed04e20631a..98a10794ca8 100644
--- a/stripe/src/main/java/com/stripe/android/StripeRequest.kt
+++ b/stripe/src/main/java/com/stripe/android/StripeRequest.kt
@@ -22,14 +22,14 @@ internal abstract class StripeRequest(
      * @return if the HTTP method is [Method.GET], return URL with query string;
      * otherwise, return the URL
      */
-    val url: String
+    internal val url: String
         @Throws(UnsupportedEncodingException::class, InvalidRequestException::class)
         get() = if (Method.GET == method) urlWithQuery() else baseUrl
 
-    val contentType: String
+    internal val contentType: String
         get() = "$mimeType; charset=$CHARSET"
 
-    val headers: Map<String, String>
+    internal val headers: Map<String, String>
         get() {
             return createHeaders()
                 .plus(HEADER_USER_AGENT to getUserAgent())
@@ -40,21 +40,22 @@ internal abstract class StripeRequest(
     @Throws(UnsupportedEncodingException::class, InvalidRequestException::class)
     internal abstract fun getOutputBytes(): ByteArray
 
-    val baseHashCode: Int
+    internal val baseHashCode: Int
         get() = Objects.hash(method, baseUrl, params)
 
     internal abstract fun createHeaders(): Map<String, String>
 
-    @Throws(InvalidRequestException::class, UnsupportedEncodingException::class)
-    fun createQuery(): String {
-        return flattenParams(params).joinToString("&") {
-            urlEncodePair(it.key, it.value)
+    internal val query: String
+        @Throws(InvalidRequestException::class, UnsupportedEncodingException::class)
+        get() {
+            return flattenParams(params).joinToString("&") {
+                urlEncodePair(it.key, it.value)
+            }
         }
-    }
 
     @Throws(InvalidRequestException::class, UnsupportedEncodingException::class)
     private fun urlWithQuery(): String {
-        val query = createQuery()
+        val query = this.query
         return if (query.isEmpty()) {
             baseUrl
         } else {
diff --git a/stripe/src/test/java/com/stripe/android/ApiRequestTest.kt b/stripe/src/test/java/com/stripe/android/ApiRequestTest.kt
index b5418e589af..274ca004df8 100644
--- a/stripe/src/test/java/com/stripe/android/ApiRequestTest.kt
+++ b/stripe/src/test/java/com/stripe/android/ApiRequestTest.kt
@@ -34,7 +34,7 @@ internal class ApiRequestTest {
         val stripeAccount = "acct_123abc"
         val headers = ApiRequest.createGet(StripeApiRepository.sourcesUrl,
             ApiRequest.Options(ApiKeyFixtures.FAKE_PUBLISHABLE_KEY,
-                stripeAccount), null)
+                stripeAccount))
             .headers
 
         assertEquals(
@@ -49,7 +49,7 @@ internal class ApiRequestTest {
     @Test
     fun getHeaders_withOnlyRequiredOptions_doesNotAddEmptyOptions() {
         val headerMap = ApiRequest.createGet(StripeApiRepository.sourcesUrl,
-            ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY), null)
+            ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY))
             .headers
 
         assertTrue(headerMap.containsKey("Stripe-Version"))
@@ -81,7 +81,7 @@ internal class ApiRequestTest {
     @Test
     fun getHeaders_correctlyAddsExpectedAdditionalParameters() {
         val headerMap = ApiRequest.createGet(StripeApiRepository.sourcesUrl,
-            ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY), null)
+            ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY))
             .headers
 
         val expectedUserAgent = "Stripe/v1 AndroidBindings/${BuildConfig.VERSION_NAME}"
@@ -94,9 +94,11 @@ internal class ApiRequestTest {
     @Throws(UnsupportedEncodingException::class, InvalidRequestException::class)
     fun createQuery_withCardData_createsProperQueryString() {
         val cardMap = NETWORK_UTILS.createCardTokenParams(CardFixtures.MINIMUM_CARD)
-        val query = ApiRequest.createGet(StripeApiRepository.sourcesUrl, ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY),
-            cardMap, null)
-            .createQuery()
+        val query = ApiRequest.createGet(
+            StripeApiRepository.sourcesUrl,
+            ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY),
+            cardMap
+        ).query
 
         val expectedValue = "muid=BF3BF4D775100923AAAFA82884FB759001162E28&product_usage=&guid=6367C48DD193D56EA7B0BAAD25B19455E529F5EE&card%5Bexp_month%5D=1&card%5Bexp_year%5D=2050&card%5Bnumber%5D=4242424242424242&card%5Bcvc%5D=123"
         assertEquals(expectedValue, query)
@@ -105,7 +107,7 @@ internal class ApiRequestTest {
     @Test
     fun getContentType() {
         val contentType = ApiRequest.createGet(StripeApiRepository.sourcesUrl,
-            ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY), null)
+            ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY))
             .contentType
         assertEquals("application/x-www-form-urlencoded; charset=UTF-8", contentType)
     }
@@ -114,7 +116,7 @@ internal class ApiRequestTest {
     @Throws(UnsupportedEncodingException::class, InvalidRequestException::class)
     fun getOutputBytes_withEmptyBody_shouldHaveZeroLength() {
         val output = ApiRequest.createPost(StripeApiRepository.paymentMethodsUrl,
-            ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY), null)
+            ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY))
             .getOutputBytes()
         assertEquals(0, output.size)
     }
@@ -124,10 +126,11 @@ internal class ApiRequestTest {
     fun getOutputBytes_withNonEmptyBody_shouldHaveNonZeroLength() {
         val params = mapOf("customer" to "cus_123")
 
-        val output = ApiRequest.createPost(StripeApiRepository.paymentMethodsUrl,
+        val output = ApiRequest.createPost(
+            StripeApiRepository.paymentMethodsUrl,
             ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY),
-            params, null)
-            .getOutputBytes()
+            params
+        ).getOutputBytes()
         assertEquals(16, output.size)
     }
 
@@ -135,22 +138,29 @@ internal class ApiRequestTest {
     fun testEquals() {
         val params = mapOf("customer" to "cus_123")
         assertEquals(
-            ApiRequest.createPost(StripeApiRepository.paymentMethodsUrl,
+            ApiRequest.createPost(
+                StripeApiRepository.paymentMethodsUrl,
                 ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY),
-                params, null),
-            ApiRequest.createPost(StripeApiRepository.paymentMethodsUrl,
+                params
+            ),
+            ApiRequest.createPost(
+                StripeApiRepository.paymentMethodsUrl,
                 ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY),
-                params, null)
+                params
+            )
         )
 
         assertNotEquals(
-            ApiRequest.createPost(StripeApiRepository.paymentMethodsUrl,
+            ApiRequest.createPost(
+                StripeApiRepository.paymentMethodsUrl,
                 ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY),
-                params, null),
-            ApiRequest.createPost(StripeApiRepository.paymentMethodsUrl,
-                ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY,
-                    "acct"),
-                params, null)
+                params
+            ),
+            ApiRequest.createPost(
+                StripeApiRepository.paymentMethodsUrl,
+                ApiRequest.Options(ApiKeyFixtures.DEFAULT_PUBLISHABLE_KEY, "acct"),
+                params
+            )
         )
     }
 
diff --git a/stripe/src/test/java/com/stripe/android/StripeTest.java b/stripe/src/test/java/com/stripe/android/StripeTest.java
index 7eb011967c2..539fae15a47 100644
--- a/stripe/src/test/java/com/stripe/android/StripeTest.java
+++ b/stripe/src/test/java/com/stripe/android/StripeTest.java
@@ -14,6 +14,7 @@
 import com.stripe.android.model.Address;
 import com.stripe.android.model.BankAccount;
 import com.stripe.android.model.Card;
+import com.stripe.android.model.CardFixtures;
 import com.stripe.android.model.PaymentMethod;
 import com.stripe.android.model.PaymentMethodCreateParams;
 import com.stripe.android.model.PaymentMethodCreateParamsFixtures;
@@ -30,6 +31,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.UUID;
 import java.util.concurrent.Executor;
 
 import org.junit.Before;
@@ -45,6 +47,7 @@
 import static com.stripe.android.CardNumberFixtures.VALID_VISA_NO_SPACES;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertThrows;
@@ -1100,6 +1103,27 @@ public void run() throws Throwable {
                 cardException.getMessage());
     }
 
+    @Test
+    public void createTokenSynchronousTwice_withIdempotencyKey_returnsSameToken()
+            throws StripeException {
+        final Stripe stripe = createStripe();
+        final String idempotencyKey = UUID.randomUUID().toString();
+        assertEquals(
+                stripe.createCardTokenSynchronous(CardFixtures.MINIMUM_CARD, idempotencyKey),
+                stripe.createCardTokenSynchronous(CardFixtures.MINIMUM_CARD, idempotencyKey)
+        );
+    }
+
+    @Test
+    public void createTokenSynchronousTwice_withoutIdempotencyKey_returnsDifferentToken()
+            throws StripeException {
+        final Stripe stripe = createStripe();
+        assertNotEquals(
+                stripe.createCardTokenSynchronous(CardFixtures.MINIMUM_CARD),
+                stripe.createCardTokenSynchronous(CardFixtures.MINIMUM_CARD)
+        );
+    }
+
     @Test
     public void createPaymentMethodSynchronous_withCard()
             throws StripeException {