diff --git a/AwsEncryptionSDK/dafny/AwsEncryptionSdk/src/Index.dfy b/AwsEncryptionSDK/dafny/AwsEncryptionSdk/src/Index.dfy
index 057ab8d96..9125c8d31 100644
--- a/AwsEncryptionSDK/dafny/AwsEncryptionSdk/src/Index.dfy
+++ b/AwsEncryptionSDK/dafny/AwsEncryptionSdk/src/Index.dfy
@@ -23,7 +23,7 @@ module
   }
 
   method ESDK(config: AwsEncryptionSdkConfig)
-    returns (res: Result<ESDKClient, Error>)
+    returns (res: Result<IAwsEncryptionSdkClient, Error>)
   {
     var maybeCrypto := Primitives.AtomicPrimitives();
     var crypto :- maybeCrypto
diff --git a/AwsEncryptionSDK/dafny/AwsEncryptionSdk/test/TestCreateEsdkClient.dfy b/AwsEncryptionSDK/dafny/AwsEncryptionSdk/test/TestCreateEsdkClient.dfy
index 1d29adba5..7f8ec2943 100644
--- a/AwsEncryptionSDK/dafny/AwsEncryptionSdk/test/TestCreateEsdkClient.dfy
+++ b/AwsEncryptionSDK/dafny/AwsEncryptionSdk/test/TestCreateEsdkClient.dfy
@@ -52,11 +52,13 @@ module TestCreateEsdkClient {
     method {:test} TestClientCreation() {
         var defaultConfig := EncryptionSdk.DefaultAwsEncryptionSdkConfig();
         
-        var esdk :- expect EncryptionSdk.ESDK(config := defaultConfig);
-        
-        expect esdk.config.commitmentPolicy == defaultConfig.commitmentPolicy.value;
-        expect esdk.config.maxEncryptedDataKeys == defaultConfig.maxEncryptedDataKeys;
-        expect esdk.config.netV4_0_0_RetryPolicy == Types.NetV4_0_0_RetryPolicy.ALLOW_RETRY;
+        var esdk: Types.IAwsEncryptionSdkClient :- expect EncryptionSdk.ESDK(config := defaultConfig);
+        expect esdk is EncryptionSdk.ESDKClient;
+        var esdkClient := esdk as EncryptionSdk.ESDKClient;
+
+        expect esdkClient.config.commitmentPolicy == defaultConfig.commitmentPolicy.value;
+        expect esdkClient.config.maxEncryptedDataKeys == defaultConfig.maxEncryptedDataKeys;
+        expect esdkClient.config.netV4_0_0_RetryPolicy == Types.NetV4_0_0_RetryPolicy.ALLOW_RETRY;
     }
 
     method {:test} TestNetRetryFlag() {