diff --git a/src/ComposerIntegration/InstalledJsonMetadata.php b/src/ComposerIntegration/InstalledJsonMetadata.php
index e91aaaaa..ee781d3b 100644
--- a/src/ComposerIntegration/InstalledJsonMetadata.php
+++ b/src/ComposerIntegration/InstalledJsonMetadata.php
@@ -4,7 +4,6 @@
 
 namespace Php\Pie\ComposerIntegration;
 
-use Composer\Package\CompletePackage;
 use Composer\Package\CompletePackageInterface;
 use Composer\PartialComposer;
 use Php\Pie\ComposerIntegration\PieInstalledJsonMetadataKeys as MetadataKey;
@@ -118,7 +117,7 @@ private function addPieMetadata(
             ->getRepositoryManager()
             ->getLocalRepository()
             ->findPackages($composerPackage->getName())[0];
-        Assert::isInstanceOf($localRepositoryPackage, CompletePackage::class);
+        Assert::methodExists($localRepositoryPackage, 'setExtra');
 
         $localRepositoryPackage->setExtra(array_merge($localRepositoryPackage->getExtra(), [$key->value => $value]));
     }
diff --git a/src/ComposerIntegration/PhpBinaryPathBasedPlatformRepository.php b/src/ComposerIntegration/PhpBinaryPathBasedPlatformRepository.php
index 15d1de73..e29f941b 100644
--- a/src/ComposerIntegration/PhpBinaryPathBasedPlatformRepository.php
+++ b/src/ComposerIntegration/PhpBinaryPathBasedPlatformRepository.php
@@ -6,6 +6,7 @@
 
 use Composer\Composer;
 use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Composer\Pcre\Preg;
 use Composer\Repository\PlatformRepository;
 use Composer\Semver\VersionParser;
@@ -85,7 +86,7 @@ public function __construct(PhpBinaryPath $phpBinaryPath, Composer $composer, In
         parent::__construct();
     }
 
-    private function packageForExtension(string $name, string $prettyVersion): CompletePackage
+    private function packageForExtension(string $name, string $prettyVersion): CompletePackageInterface
     {
         $extraDescription = '';
 
diff --git a/src/ComposerIntegration/PiePackageInstaller.php b/src/ComposerIntegration/PiePackageInstaller.php
index 65268462..bec8b961 100644
--- a/src/ComposerIntegration/PiePackageInstaller.php
+++ b/src/ComposerIntegration/PiePackageInstaller.php
@@ -6,7 +6,7 @@
 
 use Composer\Installer\LibraryInstaller;
 use Composer\IO\IOInterface;
-use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Composer\Package\PackageInterface;
 use Composer\PartialComposer;
 use Composer\Repository\InstalledRepositoryInterface;
@@ -52,7 +52,7 @@ public function install(InstalledRepositoryInterface $repo, PackageInterface $pa
                     return null;
                 }
 
-                if (! $composerPackage instanceof CompletePackage) {
+                if (! $composerPackage instanceof CompletePackageInterface) {
                     $io->writeError(sprintf(
                         '<error>Not using PIE to install %s as it was not a Complete Package</error>',
                         $composerPackage->getName(),
@@ -94,7 +94,7 @@ public function uninstall(InstalledRepositoryInterface $repo, PackageInterface $
                     return null;
                 }
 
-                if (! $composerPackage instanceof CompletePackage) {
+                if (! $composerPackage instanceof CompletePackageInterface) {
                     $io->writeError(sprintf(
                         '<error>Not using PIE to install %s as it was not a Complete Package</error>',
                         $composerPackage->getName(),
diff --git a/src/Installing/InstallForPhpProject/FindMatchingPackages.php b/src/Installing/InstallForPhpProject/FindMatchingPackages.php
index 358d9e61..5111f659 100644
--- a/src/Installing/InstallForPhpProject/FindMatchingPackages.php
+++ b/src/Installing/InstallForPhpProject/FindMatchingPackages.php
@@ -5,7 +5,7 @@
 namespace Php\Pie\Installing\InstallForPhpProject;
 
 use Composer\Composer;
-use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Composer\Repository\RepositoryInterface;
 use OutOfRangeException;
 use Php\Pie\DependencyResolver\Package;
@@ -41,7 +41,7 @@ public function for(Composer $pieComposer, string $searchTerm): array
                 static function (array $match) use ($pieComposer, $extensionName): bool {
                     $package = $pieComposer->getRepositoryManager()->findPackage($match['name'], '*');
 
-                    if (! $package instanceof CompletePackage) {
+                    if (! $package instanceof CompletePackageInterface) {
                         return false;
                     }
 
diff --git a/test/integration/Building/UnixBuildTest.php b/test/integration/Building/UnixBuildTest.php
index a8436324..73d1c80f 100644
--- a/test/integration/Building/UnixBuildTest.php
+++ b/test/integration/Building/UnixBuildTest.php
@@ -5,7 +5,7 @@
 namespace Php\PieIntegrationTest\Building;
 
 use Composer\IO\BufferIO;
-use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Composer\Util\Platform;
 use Php\Pie\Building\ExtensionBinaryNotFound;
 use Php\Pie\Building\UnixBuild;
@@ -37,7 +37,7 @@ public function testUnixBuildCanBuildExtension(): void
 
         $downloadedPackage = DownloadedPackage::fromPackageAndExtractedPath(
             new Package(
-                $this->createMock(CompletePackage::class),
+                $this->createMock(CompletePackageInterface::class),
                 ExtensionType::PhpModule,
                 ExtensionName::normaliseFromString('pie_test_ext'),
                 'pie_test_ext',
@@ -86,7 +86,7 @@ public function testUnixBuildWillThrowExceptionWhenExpectedBinaryNameMismatches(
 
         $downloadedPackage = DownloadedPackage::fromPackageAndExtractedPath(
             new Package(
-                $this->createMock(CompletePackage::class),
+                $this->createMock(CompletePackageInterface::class),
                 ExtensionType::PhpModule,
                 ExtensionName::normaliseFromString('mismatched_name'),
                 'pie_test_ext',
@@ -121,7 +121,7 @@ public function testUnixBuildCanBuildExtensionWithBuildPath(): void
 
         $output = new BufferIO();
 
-        $composerPackage = $this->createMock(CompletePackage::class);
+        $composerPackage = $this->createMock(CompletePackageInterface::class);
         $composerPackage->method('getPrettyName')->willReturn('myvendor/pie_test_ext');
         $composerPackage->method('getPrettyVersion')->willReturn('0.1.0');
         $composerPackage->method('getType')->willReturn('php-ext');
@@ -174,7 +174,7 @@ public function testCleanupDoesNotCleanWhenConfigureIsMissing(): void
 
         $downloadedPackage = DownloadedPackage::fromPackageAndExtractedPath(
             new Package(
-                $this->createMock(CompletePackage::class),
+                $this->createMock(CompletePackageInterface::class),
                 ExtensionType::PhpModule,
                 ExtensionName::normaliseFromString('pie_test_ext'),
                 'pie_test_ext',
@@ -211,7 +211,7 @@ public function testVerboseOutputShowsCleanupMessages(): void
 
         $downloadedPackage = DownloadedPackage::fromPackageAndExtractedPath(
             new Package(
-                $this->createMock(CompletePackage::class),
+                $this->createMock(CompletePackageInterface::class),
                 ExtensionType::PhpModule,
                 ExtensionName::normaliseFromString('pie_test_ext'),
                 'pie_test_ext',
diff --git a/test/integration/Downloading/GithubPackageReleaseAssetsTest.php b/test/integration/Downloading/GithubPackageReleaseAssetsTest.php
index 61f549b6..cd9cb4b3 100644
--- a/test/integration/Downloading/GithubPackageReleaseAssetsTest.php
+++ b/test/integration/Downloading/GithubPackageReleaseAssetsTest.php
@@ -6,7 +6,7 @@
 
 use Composer\Factory;
 use Composer\IO\NullIO;
-use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Composer\Util\HttpDownloader;
 use Php\Pie\DependencyResolver\Package;
 use Php\Pie\Downloading\GithubPackageReleaseAssets;
@@ -46,7 +46,7 @@ public function testDeterminingReleaseAssetUrlForWindows(): void
         );
 
         $package = new Package(
-            $this->createMock(CompletePackage::class),
+            $this->createMock(CompletePackageInterface::class),
             ExtensionType::PhpModule,
             ExtensionName::normaliseFromString('example_pie_extension'),
             'asgrim/example-pie-extension',
diff --git a/test/integration/Installing/UnixInstallTest.php b/test/integration/Installing/UnixInstallTest.php
index 7709cddf..cd58849f 100644
--- a/test/integration/Installing/UnixInstallTest.php
+++ b/test/integration/Installing/UnixInstallTest.php
@@ -5,7 +5,7 @@
 namespace Php\PieIntegrationTest\Installing;
 
 use Composer\IO\BufferIO;
-use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Composer\Util\Platform;
 use Php\Pie\Building\UnixBuild;
 use Php\Pie\DependencyResolver\Package;
@@ -78,7 +78,7 @@ public function testUnixInstallCanInstallExtension(string $phpConfig): void
 
         $downloadedPackage = DownloadedPackage::fromPackageAndExtractedPath(
             new Package(
-                $this->createMock(CompletePackage::class),
+                $this->createMock(CompletePackageInterface::class),
                 ExtensionType::PhpModule,
                 ExtensionName::normaliseFromString('pie_test_ext'),
                 'pie_test_ext',
diff --git a/test/integration/Installing/WindowsInstallTest.php b/test/integration/Installing/WindowsInstallTest.php
index 0f6c2fad..086fe026 100644
--- a/test/integration/Installing/WindowsInstallTest.php
+++ b/test/integration/Installing/WindowsInstallTest.php
@@ -5,7 +5,7 @@
 namespace Php\PieIntegrationTest\Installing;
 
 use Composer\IO\BufferIO;
-use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Php\Pie\DependencyResolver\Package;
 use Php\Pie\Downloading\DownloadedPackage;
 use Php\Pie\ExtensionName;
@@ -47,7 +47,7 @@ public function testWindowsInstallCanInstallExtension(): void
     {
         $downloadedPackage = DownloadedPackage::fromPackageAndExtractedPath(
             new Package(
-                $this->createMock(CompletePackage::class),
+                $this->createMock(CompletePackageInterface::class),
                 ExtensionType::PhpModule,
                 ExtensionName::normaliseFromString('pie_test_ext'),
                 'php/pie-test-ext',
diff --git a/test/unit/Command/CommandHelperTest.php b/test/unit/Command/CommandHelperTest.php
index 98b1c743..04c1f1ee 100644
--- a/test/unit/Command/CommandHelperTest.php
+++ b/test/unit/Command/CommandHelperTest.php
@@ -7,7 +7,7 @@
 use Composer\Composer;
 use Composer\IO\BufferIO;
 use Composer\IO\NullIO;
-use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Composer\Repository\ComposerRepository;
 use Composer\Repository\PathRepository;
 use Composer\Repository\RepositoryManager;
@@ -95,7 +95,7 @@ public function testBindingConfigurationOptionsFromPackage(): void
 
     public function testProcessingConfigureOptionsFromInput(): void
     {
-        $composerPackage = $this->createMock(CompletePackage::class);
+        $composerPackage = $this->createMock(CompletePackageInterface::class);
         $composerPackage->method('getPrettyName')->willReturn('foo/bar');
         $composerPackage->method('getPrettyVersion')->willReturn('1.0.0');
         $composerPackage->method('getType')->willReturn('php-ext');
diff --git a/test/unit/ComposerIntegration/InstalledJsonMetadataTest.php b/test/unit/ComposerIntegration/InstalledJsonMetadataTest.php
index dead5ba2..c1dc4cd5 100644
--- a/test/unit/ComposerIntegration/InstalledJsonMetadataTest.php
+++ b/test/unit/ComposerIntegration/InstalledJsonMetadataTest.php
@@ -7,6 +7,7 @@
 use Composer\Composer;
 use Composer\IO\IOInterface;
 use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Composer\Repository\InstalledArrayRepository;
 use Composer\Repository\RepositoryManager;
 use Php\Pie\ComposerIntegration\InstalledJsonMetadata;
@@ -28,7 +29,7 @@
 #[CoversClass(InstalledJsonMetadata::class)]
 final class InstalledJsonMetadataTest extends TestCase
 {
-    private function mockComposerInstalledRepositoryWith(CompletePackage $package): Composer&MockObject
+    private function mockComposerInstalledRepositoryWith(CompletePackageInterface $package): Composer&MockObject
     {
         $installedRepository = new InstalledArrayRepository([$package]);
 
diff --git a/test/unit/DependencyResolver/PackageTest.php b/test/unit/DependencyResolver/PackageTest.php
index 3889d755..ea8b3080 100644
--- a/test/unit/DependencyResolver/PackageTest.php
+++ b/test/unit/DependencyResolver/PackageTest.php
@@ -5,6 +5,7 @@
 namespace Php\PieUnitTest\DependencyResolver;
 
 use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use InvalidArgumentException;
 use Php\Pie\DependencyResolver\Package;
 use Php\Pie\ExtensionName;
@@ -124,7 +125,7 @@ public static function githubOrgAndRepoFromPackage(): array
     public function testGithubOrgAndRepo(string $composerPackageName, string|null $downloadUrl, string $expectedGithubOrgAndRepo): void
     {
         $package = new Package(
-            $this->createMock(CompletePackage::class),
+            $this->createMock(CompletePackageInterface::class),
             ExtensionType::PhpModule,
             ExtensionName::normaliseFromString('foo'),
             $composerPackageName,
diff --git a/test/unit/Downloading/DownloadUrlMethodTest.php b/test/unit/Downloading/DownloadUrlMethodTest.php
index d3856006..26712bec 100644
--- a/test/unit/Downloading/DownloadUrlMethodTest.php
+++ b/test/unit/Downloading/DownloadUrlMethodTest.php
@@ -4,7 +4,6 @@
 
 namespace Php\PieUnitTest\Downloading;
 
-use Composer\Package\CompletePackage;
 use Composer\Package\CompletePackageInterface;
 use Php\Pie\DependencyResolver\Package;
 use Php\Pie\Downloading\DownloadUrlMethod;
@@ -64,7 +63,7 @@ public function testWindowsPackages(): void
 
     public function testPrePackagedSourceDownloads(): void
     {
-        $composerPackage = $this->createMock(CompletePackage::class);
+        $composerPackage = $this->createMock(CompletePackageInterface::class);
         $composerPackage->method('getPrettyName')->willReturn('foo/bar');
         $composerPackage->method('getPrettyVersion')->willReturn('1.2.3');
         $composerPackage->method('getType')->willReturn('php-ext');
diff --git a/test/unit/Downloading/DownloadedPackageTest.php b/test/unit/Downloading/DownloadedPackageTest.php
index 4ffb581e..ea8b306c 100644
--- a/test/unit/Downloading/DownloadedPackageTest.php
+++ b/test/unit/Downloading/DownloadedPackageTest.php
@@ -4,7 +4,7 @@
 
 namespace Php\PieUnitTest\Downloading;
 
-use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Php\Pie\DependencyResolver\Package;
 use Php\Pie\Downloading\DownloadedPackage;
 use Php\Pie\ExtensionName;
@@ -23,7 +23,7 @@ final class DownloadedPackageTest extends TestCase
     public function testFromPackageAndExtractedPath(): void
     {
         $package = new Package(
-            $this->createMock(CompletePackage::class),
+            $this->createMock(CompletePackageInterface::class),
             ExtensionType::PhpModule,
             ExtensionName::normaliseFromString('foo'),
             'foo/bar',
@@ -41,7 +41,7 @@ public function testFromPackageAndExtractedPath(): void
 
     public function testFromPackageAndExtractedPathWithBuildPath(): void
     {
-        $composerPackage = $this->createMock(CompletePackage::class);
+        $composerPackage = $this->createMock(CompletePackageInterface::class);
         $composerPackage->method('getPrettyName')->willReturn('foo/bar');
         $composerPackage->method('getPrettyVersion')->willReturn('1.2.3');
         $composerPackage->method('getType')->willReturn('php-ext');
@@ -59,7 +59,7 @@ public function testFromPackageAndExtractedPathWithBuildPath(): void
 
     public function testFromPackageAndExtractedPathWithBuildPathWithVersionTemplate(): void
     {
-        $composerPackage = $this->createMock(CompletePackage::class);
+        $composerPackage = $this->createMock(CompletePackageInterface::class);
         $composerPackage->method('getPrettyName')->willReturn('foo/bar');
         $composerPackage->method('getPrettyVersion')->willReturn('1.2.3');
         $composerPackage->method('getType')->willReturn('php-ext');
@@ -77,7 +77,7 @@ public function testFromPackageAndExtractedPathWithBuildPathWithVersionTemplate(
 
     public function testBuildPathDetectedFromExtractedPrePackagedSourceAsset(): void
     {
-        $composerPackage = $this->createMock(CompletePackage::class);
+        $composerPackage = $this->createMock(CompletePackageInterface::class);
         $composerPackage->method('getPrettyName')->willReturn('foo/bar');
         $composerPackage->method('getPrettyVersion')->willReturn('1.2.3');
         $composerPackage->method('getType')->willReturn('php-ext');
diff --git a/test/unit/Downloading/Exception/CouldNotFindReleaseAssetTest.php b/test/unit/Downloading/Exception/CouldNotFindReleaseAssetTest.php
index 83bc674d..d7b153d3 100644
--- a/test/unit/Downloading/Exception/CouldNotFindReleaseAssetTest.php
+++ b/test/unit/Downloading/Exception/CouldNotFindReleaseAssetTest.php
@@ -4,7 +4,7 @@
 
 namespace Php\PieUnitTest\Downloading\Exception;
 
-use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Php\Pie\DependencyResolver\Package;
 use Php\Pie\Downloading\Exception\CouldNotFindReleaseAsset;
 use Php\Pie\ExtensionName;
@@ -25,7 +25,7 @@ final class CouldNotFindReleaseAssetTest extends TestCase
     public function testForPackageWithRegularPackage(): void
     {
         $package = new Package(
-            $this->createMock(CompletePackage::class),
+            $this->createMock(CompletePackageInterface::class),
             ExtensionType::PhpModule,
             ExtensionName::normaliseFromString('foo'),
             'foo/bar',
@@ -53,7 +53,7 @@ public function testForPackageWithRegularPackage(): void
     public function testForPackageWithWindowsPackage(): void
     {
         $package = new Package(
-            $this->createMock(CompletePackage::class),
+            $this->createMock(CompletePackageInterface::class),
             ExtensionType::PhpModule,
             ExtensionName::normaliseFromString('foo'),
             'foo/bar',
@@ -81,7 +81,7 @@ public function testForPackageWithWindowsPackage(): void
     public function testForPackageWithMissingTag(): void
     {
         $package = new Package(
-            $this->createMock(CompletePackage::class),
+            $this->createMock(CompletePackageInterface::class),
             ExtensionType::PhpModule,
             ExtensionName::normaliseFromString('foo'),
             'foo/bar',
diff --git a/test/unit/Downloading/GithubPackageReleaseAssetsTest.php b/test/unit/Downloading/GithubPackageReleaseAssetsTest.php
index d19b55db..eb2985fd 100644
--- a/test/unit/Downloading/GithubPackageReleaseAssetsTest.php
+++ b/test/unit/Downloading/GithubPackageReleaseAssetsTest.php
@@ -5,7 +5,7 @@
 namespace Php\PieUnitTest\Downloading;
 
 use Composer\Downloader\TransportException;
-use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Composer\Util\Http\Response;
 use Composer\Util\HttpDownloader;
 use Php\Pie\DependencyResolver\Package;
@@ -70,7 +70,7 @@ public function testUrlIsReturnedWhenFindingWindowsDownloadUrl(): void
             ->willReturn($httpDownloaderResponse);
 
         $package = new Package(
-            $this->createMock(CompletePackage::class),
+            $this->createMock(CompletePackageInterface::class),
             ExtensionType::PhpModule,
             ExtensionName::normaliseFromString('foo'),
             'asgrim/example-pie-extension',
@@ -135,7 +135,7 @@ public function testUrlIsReturnedWhenFindingWindowsDownloadUrlWithCompilerAndThr
             ->willReturn($httpDownloaderResponse);
 
         $package = new Package(
-            $this->createMock(CompletePackage::class),
+            $this->createMock(CompletePackageInterface::class),
             ExtensionType::PhpModule,
             ExtensionName::normaliseFromString('foo'),
             'asgrim/example-pie-extension',
@@ -181,7 +181,7 @@ public function testFindWindowsDownloadUrlForPackageThrowsExceptionWhenAssetNotF
             ->willThrowException($e);
 
         $package = new Package(
-            $this->createMock(CompletePackage::class),
+            $this->createMock(CompletePackageInterface::class),
             ExtensionType::PhpModule,
             ExtensionName::normaliseFromString('foo'),
             'asgrim/example-pie-extension',
diff --git a/test/unit/Installing/Ini/AddExtensionToTheIniFileTest.php b/test/unit/Installing/Ini/AddExtensionToTheIniFileTest.php
index d2a71a7b..afe7a9b9 100644
--- a/test/unit/Installing/Ini/AddExtensionToTheIniFileTest.php
+++ b/test/unit/Installing/Ini/AddExtensionToTheIniFileTest.php
@@ -5,7 +5,7 @@
 namespace Php\PieUnitTest\Installing\Ini;
 
 use Composer\IO\BufferIO;
-use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Php\Pie\DependencyResolver\Package;
 use Php\Pie\ExtensionName;
 use Php\Pie\ExtensionType;
@@ -59,7 +59,7 @@ public function testReturnsFalseWhenFileIsNotWritableAndSudoDoesNotExist(): void
             self::assertFalse((new AddExtensionToTheIniFile())(
                 $unwritableFilename,
                 new Package(
-                    $this->createMock(CompletePackage::class),
+                    $this->createMock(CompletePackageInterface::class),
                     ExtensionType::PhpModule,
                     ExtensionName::normaliseFromString('foobar'),
                     'foo/bar',
@@ -95,7 +95,7 @@ public function testReturnsTrueWhenFileIsNotWritableAndSudoExists(): void
             self::assertTrue((new AddExtensionToTheIniFile())(
                 $unwritableFilename,
                 new Package(
-                    $this->createMock(CompletePackage::class),
+                    $this->createMock(CompletePackageInterface::class),
                     ExtensionType::PhpModule,
                     ExtensionName::normaliseFromString('foobar'),
                     'foo/bar',
@@ -127,7 +127,7 @@ public function testReturnsFalseWhenExistingIniCouldNotBeRead(): void
             self::assertFalse((new AddExtensionToTheIniFile())(
                 $unreadableIniFile,
                 new Package(
-                    $this->createMock(CompletePackage::class),
+                    $this->createMock(CompletePackageInterface::class),
                     ExtensionType::PhpModule,
                     ExtensionName::normaliseFromString('foobar'),
                     'foo/bar',
@@ -170,7 +170,7 @@ public function testReturnsFalseWhenExtensionWasAddedButPhpRuntimeDidNotLoadExte
             self::assertFalse((new AddExtensionToTheIniFile())(
                 $iniFile,
                 new Package(
-                    $this->createMock(CompletePackage::class),
+                    $this->createMock(CompletePackageInterface::class),
                     ExtensionType::PhpModule,
                     $extensionName,
                     'foo/bar',
@@ -207,7 +207,7 @@ public function testReturnsTrueWhenExtensionAdded(): void
             self::assertTrue((new AddExtensionToTheIniFile())(
                 $iniFile,
                 new Package(
-                    $this->createMock(CompletePackage::class),
+                    $this->createMock(CompletePackageInterface::class),
                     ExtensionType::PhpModule,
                     ExtensionName::normaliseFromString('foobar'),
                     'foo/bar',
@@ -250,7 +250,7 @@ public function testReturnsTrueWhenExtensionAddedWithAdditionalStep(): void
             self::assertTrue((new AddExtensionToTheIniFile())(
                 $iniFile,
                 new Package(
-                    $this->createMock(CompletePackage::class),
+                    $this->createMock(CompletePackageInterface::class),
                     ExtensionType::PhpModule,
                     ExtensionName::normaliseFromString('foobar'),
                     'foo/bar',
diff --git a/test/unit/Installing/Ini/PickBestSetupIniApproachTest.php b/test/unit/Installing/Ini/PickBestSetupIniApproachTest.php
index ff3dd5c2..151c5cdf 100644
--- a/test/unit/Installing/Ini/PickBestSetupIniApproachTest.php
+++ b/test/unit/Installing/Ini/PickBestSetupIniApproachTest.php
@@ -5,7 +5,7 @@
 namespace Php\PieUnitTest\Installing\Ini;
 
 use Composer\IO\BufferIO;
-use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Php\Pie\DependencyResolver\Package;
 use Php\Pie\Downloading\DownloadedPackage;
 use Php\Pie\ExtensionName;
@@ -92,7 +92,7 @@ public function testVerboseMessageIsEmittedSettingUpWithoutAnyApproaches(): void
             $this->targetPlatform(),
             DownloadedPackage::fromPackageAndExtractedPath(
                 new Package(
-                    $this->createMock(CompletePackage::class),
+                    $this->createMock(CompletePackageInterface::class),
                     ExtensionType::PhpModule,
                     ExtensionName::normaliseFromString('foo'),
                     'test-vendor/test-package',
@@ -127,7 +127,7 @@ public function testWorkingApproachIsUsed(): void
             $this->targetPlatform(),
             DownloadedPackage::fromPackageAndExtractedPath(
                 new Package(
-                    $this->createMock(CompletePackage::class),
+                    $this->createMock(CompletePackageInterface::class),
                     ExtensionType::PhpModule,
                     ExtensionName::normaliseFromString('foo'),
                     'test-vendor/test-package',
@@ -162,7 +162,7 @@ public function testSetupFailsWhenNoApproachesWork(): void
             $this->targetPlatform(),
             DownloadedPackage::fromPackageAndExtractedPath(
                 new Package(
-                    $this->createMock(CompletePackage::class),
+                    $this->createMock(CompletePackageInterface::class),
                     ExtensionType::PhpModule,
                     ExtensionName::normaliseFromString('foo'),
                     'test-vendor/test-package',
diff --git a/test/unit/Installing/InstallForPhpProject/FindMatchingPackagesTest.php b/test/unit/Installing/InstallForPhpProject/FindMatchingPackagesTest.php
index 583f9de8..d3032d86 100644
--- a/test/unit/Installing/InstallForPhpProject/FindMatchingPackagesTest.php
+++ b/test/unit/Installing/InstallForPhpProject/FindMatchingPackagesTest.php
@@ -8,6 +8,7 @@
 use Composer\Config;
 use Composer\IO\IOInterface;
 use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Composer\Repository\ArrayRepository;
 use Composer\Repository\RepositoryManager;
 use Composer\Util\HttpDownloader;
@@ -22,7 +23,7 @@ final class FindMatchingPackagesTest extends TestCase
     public function testSearchResultsAreFilteredByExtensionName(): void
     {
         $repository = new ArrayRepository([
-            (static function (): CompletePackage {
+            (static function (): CompletePackageInterface {
                 $package = new CompletePackage('another/bar', '1.5.0.0', '1.5.0');
                 $package->setDescription('These are not the extensions you are looking for');
                 $package->setType(ExtensionType::PhpModule->value);
@@ -30,14 +31,14 @@ public function testSearchResultsAreFilteredByExtensionName(): void
 
                 return $package;
             })(),
-            (static function (): CompletePackage {
+            (static function (): CompletePackageInterface {
                 $package = new CompletePackage('foo/bar', '1.2.3.0', '1.2.3');
                 $package->setDescription('The best extension there is');
                 $package->setType(ExtensionType::PhpModule->value);
 
                 return $package;
             })(),
-            (static function (): CompletePackage {
+            (static function (): CompletePackageInterface {
                 $package = new CompletePackage('foo/bar', '2.0.0.0', '2.0.0');
                 $package->setDescription('The best extension there is');
                 $package->setType(ExtensionType::PhpModule->value);
diff --git a/test/unit/Platform/WindowsExtensionAssetNameTest.php b/test/unit/Platform/WindowsExtensionAssetNameTest.php
index 77a77764..446b8a3d 100644
--- a/test/unit/Platform/WindowsExtensionAssetNameTest.php
+++ b/test/unit/Platform/WindowsExtensionAssetNameTest.php
@@ -4,7 +4,7 @@
 
 namespace Php\PieUnitTest\Platform;
 
-use Composer\Package\CompletePackage;
+use Composer\Package\CompletePackageInterface;
 use Php\Pie\DependencyResolver\Package;
 use Php\Pie\ExtensionName;
 use Php\Pie\ExtensionType;
@@ -43,7 +43,7 @@ public function setUp(): void
         $this->phpVersion = $this->platform->phpBinaryPath->majorMinorVersion();
 
         $this->package = new Package(
-            $this->createMock(CompletePackage::class),
+            $this->createMock(CompletePackageInterface::class),
             ExtensionType::PhpModule,
             ExtensionName::normaliseFromString('foo'),
             'phpf/foo',