diff --git a/.github/workflows/phpunit.yml b/.github/workflows/phpunit.yml
index a306550..f25a183 100644
--- a/.github/workflows/phpunit.yml
+++ b/.github/workflows/phpunit.yml
@@ -24,6 +24,7 @@ jobs:
           - "8.1"
           - "8.2"
           - "8.3"
+          - "8.4"
 
         include:
           - php-version: '7.2'
@@ -49,5 +50,10 @@ jobs:
         if: ${{ matrix.dependencies == 'highest' }}
         run: "composer update --no-interaction --no-progress"
 
-      - name: "Tests"
+      - name: "Tests (PHPUnit 9)"
+        if: ${{ matrix.php-version <= '8.0' }}
+        run: "vendor/bin/phpunit --configuration phpunit9.xml.dist"
+
+      - name: "Tests (PHPUnit 10+)"
+        if: ${{ matrix.php-version >= '8.1' }}
         run: "vendor/bin/phpunit"
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index ab4e9d3..21263b8 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,26 +1,24 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.5/phpunit.xsd"
          bootstrap="vendor/autoload.php"
          backupGlobals="false"
-         backupStaticAttributes="false"
+         backupStaticProperties="false"
          colors="true"
-         verbose="true"
-         convertErrorsToExceptions="true"
-         convertNoticesToExceptions="true"
-         convertWarningsToExceptions="true"
          processIsolation="false"
-         stopOnFailure="false"
-         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd">
+         stopOnFailure="false">
   <coverage>
-    <include>
-      <directory suffix=".php">src/</directory>
-    </include>
     <report>
       <clover outputFile="build/logs/clover.xml"/>
       <html outputDirectory="build/coverage"/>
       <text outputFile="build/coverage.txt"/>
     </report>
   </coverage>
+  <source restrictDeprecations="true" restrictNotices="true" restrictWarnings="true">
+    <include>
+      <directory suffix=".php">src/</directory>
+    </include>
+  </source>
   <testsuites>
     <testsuite name="Omnipay Test Suite">
       <directory>tests</directory>
diff --git a/phpunit9.xml.dist b/phpunit9.xml.dist
new file mode 100644
index 0000000..ab4e9d3
--- /dev/null
+++ b/phpunit9.xml.dist
@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         bootstrap="vendor/autoload.php"
+         backupGlobals="false"
+         backupStaticAttributes="false"
+         colors="true"
+         verbose="true"
+         convertErrorsToExceptions="true"
+         convertNoticesToExceptions="true"
+         convertWarningsToExceptions="true"
+         processIsolation="false"
+         stopOnFailure="false"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd">
+  <coverage>
+    <include>
+      <directory suffix=".php">src/</directory>
+    </include>
+    <report>
+      <clover outputFile="build/logs/clover.xml"/>
+      <html outputDirectory="build/coverage"/>
+      <text outputFile="build/coverage.txt"/>
+    </report>
+  </coverage>
+  <testsuites>
+    <testsuite name="Omnipay Test Suite">
+      <directory>tests</directory>
+    </testsuite>
+  </testsuites>
+  <logging>
+    <junit outputFile="build/report.junit.xml"/>
+  </logging>
+</phpunit>
diff --git a/src/Common/Http/Client.php b/src/Common/Http/Client.php
index e20a610..7eece58 100644
--- a/src/Common/Http/Client.php
+++ b/src/Common/Http/Client.php
@@ -2,7 +2,6 @@
 
 namespace Omnipay\Common\Http;
 
-use function GuzzleHttp\Psr7\str;
 use Http\Client\HttpClient;
 use Http\Discovery\HttpClientDiscovery;
 use Http\Discovery\MessageFactoryDiscovery;
@@ -12,7 +11,6 @@
 use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\StreamInterface;
-use Psr\Http\Message\UriInterface;
 
 class Client implements ClientInterface
 {
