diff --git a/composer.json b/composer.json
index 66f087b..1464712 100644
--- a/composer.json
+++ b/composer.json
@@ -10,7 +10,8 @@
         }
     ],
     "require": {
-        "php": ">=7.4 <9.0"
+        "php": ">=7.4 <9.0",
+        "ext-json": "*"
     },
     "require-dev": {
         "phpunit/phpunit": "^9.6",
@@ -33,7 +34,7 @@
     },
     "scripts": {
         "phpcbf": "./vendor/bin/phpcbf",
-        "phpcs": "./vendor/bin/phpcs",
+        "phpcs": "./vendor/bin/phpcs -s",
         "rector": "./vendor/bin/rector process",
         "rector-dry-run": "./vendor/bin/rector process --dry-run",
         "test": "./vendor/bin/phpunit --testsuite all"
diff --git a/phpcs.xml b/phpcs.xml
index 45200cd..9061a78 100644
--- a/phpcs.xml
+++ b/phpcs.xml
@@ -8,7 +8,10 @@
     <file>test</file>
     <file>rector.php</file>
 
-    <rule ref="PSR1"/>
+    <rule ref="PSR1">
+        <!-- PSR1 does not like that we trigger deprecation errors. -->
+        <exclude name="PSR1.Files.SideEffects.FoundWithSymbols"/>
+    </rule>
     <rule ref="PSR2"/>
 
 </ruleset>
diff --git a/phpunit.xml b/phpunit.xml
index eceeba6..5bd7600 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -1,6 +1,8 @@
 <?xml version="1.0"?>
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd" verbose="false">
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.6/phpunit.xsd"
+         verbose="false"
+         colors="true">
     <coverage processUncoveredFiles="true">
         <include>
             <directory suffix=".php">src</directory>
@@ -11,7 +13,7 @@
     </listeners>
     <php>
         <!-- Don't fail for external dependencies. -->
-        <env name="SYMFONY_DEPRECATIONS_HELPER" value="max[self]=0"/>
+        <env name="SYMFONY_DEPRECATIONS_HELPER" value="disabled"/>
     </php>
     <testsuites>
         <testsuite name="all">
diff --git a/src/CountableInterface.php b/src/CountableInterface.php
index 358c85e..12825f4 100644
--- a/src/CountableInterface.php
+++ b/src/CountableInterface.php
@@ -2,6 +2,8 @@
 
 namespace Contracts;
 
+@trigger_error(__NAMESPACE__ . '\CountableInterface is deprecated. Use \Countable instead.', E_USER_DEPRECATED);
+
 interface CountableInterface
 {
     public function count(): int;
diff --git a/src/HydratableInterface.php b/src/HydratableInterface.php
index 30b8f45..f9efc78 100644
--- a/src/HydratableInterface.php
+++ b/src/HydratableInterface.php
@@ -2,6 +2,11 @@
 
 namespace Contracts;
 
+@trigger_error(
+    __NAMESPACE__ . '\HydratableInterface is deprecated. Use \Procrastinator\HydratableInterface intead.',
+    E_USER_DEPRECATED
+);
+
 interface HydratableInterface extends \JsonSerializable
 {
     public static function hydrate(string $json, $instance = null);
diff --git a/src/ParserInterface.php b/src/ParserInterface.php
index f39cabd..ad225c2 100644
--- a/src/ParserInterface.php
+++ b/src/ParserInterface.php
@@ -3,6 +3,11 @@
 
 namespace Contracts;
 
+@trigger_error(
+    __NAMESPACE__ . '\ParserInterface is deprecated. Use \CsvParser\Parser\ParserInterface intead.',
+    E_USER_DEPRECATED
+);
+
 interface ParserInterface
 {
     public function feed(string $chunk);