diff --git a/composer.lock b/composer.lock
index 2e962dd..02f1d4b 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4900,16 +4900,16 @@
         },
         {
             "name": "php-coveralls/php-coveralls",
-            "version": "v2.4.2",
+            "version": "v2.4.3",
             "source": {
                 "type": "git",
                 "url": "https://github.com/php-coveralls/php-coveralls.git",
-                "reference": "8a33ae229da63a0bd22dadae1512af663ce5e559"
+                "reference": "909381bd40a17ae6e9076051f0d73293c1c091af"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/php-coveralls/php-coveralls/zipball/8a33ae229da63a0bd22dadae1512af663ce5e559",
-                "reference": "8a33ae229da63a0bd22dadae1512af663ce5e559",
+                "url": "https://api.github.com/repos/php-coveralls/php-coveralls/zipball/909381bd40a17ae6e9076051f0d73293c1c091af",
+                "reference": "909381bd40a17ae6e9076051f0d73293c1c091af",
                 "shasum": ""
             },
             "require": {
@@ -4977,9 +4977,9 @@
             ],
             "support": {
                 "issues": "https://github.com/php-coveralls/php-coveralls/issues",
-                "source": "https://github.com/php-coveralls/php-coveralls/tree/v2.4.2"
+                "source": "https://github.com/php-coveralls/php-coveralls/tree/v2.4.3"
             },
-            "time": "2020-10-23T16:34:35+00:00"
+            "time": "2020-12-24T09:17:03+00:00"
         },
         {
             "name": "php-parallel-lint/php-console-color",
diff --git a/src/Message/Call.php b/src/Message/Call.php
index e92228a..b04e2c3 100644
--- a/src/Message/Call.php
+++ b/src/Message/Call.php
@@ -6,7 +6,7 @@
 
 use parallel\Channel;
 
-final class Call
+final class Call implements Message
 {
     private Channel $channel;
 
diff --git a/src/Message/Destruct.php b/src/Message/Destruct.php
index 06d4654..53e914f 100644
--- a/src/Message/Destruct.php
+++ b/src/Message/Destruct.php
@@ -4,7 +4,7 @@
 
 namespace ReactParallel\ObjectProxy\Message;
 
-final class Destruct
+final class Destruct implements Message
 {
     private string $hash;
     private string $objectHash;
diff --git a/src/Message/Existence.php b/src/Message/Existence.php
index f23de79..643f34c 100644
--- a/src/Message/Existence.php
+++ b/src/Message/Existence.php
@@ -4,7 +4,7 @@
 
 namespace ReactParallel\ObjectProxy\Message;
 
-final class Existence
+final class Existence implements Message
 {
     private string $hash;
     private string $objectHash;
diff --git a/src/Message/Link.php b/src/Message/Link.php
index 9d544b9..47b1d16 100644
--- a/src/Message/Link.php
+++ b/src/Message/Link.php
@@ -4,7 +4,7 @@
 
 namespace ReactParallel\ObjectProxy\Message;
 
-final class Link
+final class Link implements Message
 {
     private string $hash;
     private string $objectHash;
diff --git a/src/Message/Message.php b/src/Message/Message.php
new file mode 100644
index 0000000..058e2ac
--- /dev/null
+++ b/src/Message/Message.php
@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace ReactParallel\ObjectProxy\Message;
+
+interface Message
+{
+    public function hash(): string;
+
+    public function objectHash(): string;
+}
diff --git a/src/Message/Notify.php b/src/Message/Notify.php
index 5953790..746e8be 100644
--- a/src/Message/Notify.php
+++ b/src/Message/Notify.php
@@ -4,7 +4,7 @@
 
 namespace ReactParallel\ObjectProxy\Message;
 
-final class Notify
+final class Notify implements Message
 {
     private string $hash;
     private string $objectHash;