diff --git a/src/ComposerIntegration/ComposerIntegrationHandler.php b/src/ComposerIntegration/ComposerIntegrationHandler.php
index 64a5561..d5e33ca 100644
--- a/src/ComposerIntegration/ComposerIntegrationHandler.php
+++ b/src/ComposerIntegration/ComposerIntegrationHandler.php
@@ -55,6 +55,7 @@ public function __invoke(Package $package, Composer $composer, TargetPlatform $t
 
         $composerInstaller = PieComposerInstaller::createWithPhpBinary(
             $targetPlatform->phpBinaryPath,
+            $package->extensionName,
             $this->arrayCollectionIo,
             $composer,
         );
diff --git a/src/ComposerIntegration/PhpBinaryPathBasedPlatformRepository.php b/src/ComposerIntegration/PhpBinaryPathBasedPlatformRepository.php
index 72e75de..fae9d17 100644
--- a/src/ComposerIntegration/PhpBinaryPathBasedPlatformRepository.php
+++ b/src/ComposerIntegration/PhpBinaryPathBasedPlatformRepository.php
@@ -8,6 +8,7 @@
 use Composer\Pcre\Preg;
 use Composer\Repository\PlatformRepository;
 use Composer\Semver\VersionParser;
+use Php\Pie\ExtensionName;
 use Php\Pie\Platform\TargetPhp\PhpBinaryPath;
 use UnexpectedValueException;
 
@@ -19,7 +20,7 @@ class PhpBinaryPathBasedPlatformRepository extends PlatformRepository
 {
     private VersionParser $versionParser;
 
-    public function __construct(PhpBinaryPath $phpBinaryPath)
+    public function __construct(PhpBinaryPath $phpBinaryPath, ExtensionName|null $extensionBeingInstalled)
     {
         $this->versionParser = new VersionParser();
         $this->packages      = [];
@@ -32,6 +33,16 @@ public function __construct(PhpBinaryPath $phpBinaryPath)
         $extVersions = $phpBinaryPath->extensions();
 
         foreach ($extVersions as $extension => $extensionVersion) {
+            /**
+             * If the extension we're trying to exclude is not excluded from this list if it is already installed
+             * and enabled, it conflicts when running {@see ComposerIntegrationHandler}.
+             *
+             * @link https://github.com/php/pie/issues/150
+             */
+            if ($extensionBeingInstalled !== null && $extension === $extensionBeingInstalled->name()) {
+                continue;
+            }
+
             $this->addPackage($this->packageForExtension($extension, $extensionVersion));
         }
 
diff --git a/src/ComposerIntegration/PieComposerInstaller.php b/src/ComposerIntegration/PieComposerInstaller.php
index 524d504..57febc0 100644
--- a/src/ComposerIntegration/PieComposerInstaller.php
+++ b/src/ComposerIntegration/PieComposerInstaller.php
@@ -8,6 +8,7 @@
 use Composer\Installer;
 use Composer\IO\IOInterface;
 use Composer\Repository\PlatformRepository;
+use Php\Pie\ExtensionName;
 use Php\Pie\Platform\TargetPhp\PhpBinaryPath;
 use Webmozart\Assert\Assert;
 
@@ -18,17 +19,23 @@
  */
 class PieComposerInstaller extends Installer
 {
-    private PhpBinaryPath|null $phpBinaryPath = null;
+    private PhpBinaryPath|null $phpBinaryPath           = null;
+    private ExtensionName|null $extensionBeingInstalled = null;
 
     protected function createPlatformRepo(bool $forUpdate): PlatformRepository
     {
-        Assert::notNull($this->phpBinaryPath, 'PHP Binary path was not set, maybe createWithPhpBinary was not used?');
+        Assert::notNull($this->phpBinaryPath, '$phpBinaryPath was not set, maybe createWithPhpBinary was not used?');
+        Assert::notNull($this->extensionBeingInstalled, '$extensionBeingInstalled was not set, maybe createWithPhpBinary was not used?');
 
-        return new PhpBinaryPathBasedPlatformRepository($this->phpBinaryPath);
+        return new PhpBinaryPathBasedPlatformRepository($this->phpBinaryPath, $this->extensionBeingInstalled);
     }
 
-    public static function createWithPhpBinary(PhpBinaryPath $php, IOInterface $io, Composer $composer): self
-    {
+    public static function createWithPhpBinary(
+        PhpBinaryPath $php,
+        ExtensionName $extensionBeingInstalled,
+        IOInterface $io,
+        Composer $composer,
+    ): self {
         /** @psalm-suppress InvalidArgument some kind of unrelated type mismatch, defined in parent */
         $composerInstaller = new self(
             $io,
@@ -42,7 +49,8 @@ public static function createWithPhpBinary(PhpBinaryPath $php, IOInterface $io,
             $composer->getAutoloadGenerator(),
         );
 
-        $composerInstaller->phpBinaryPath = $php;
+        $composerInstaller->phpBinaryPath           = $php;
+        $composerInstaller->extensionBeingInstalled = $extensionBeingInstalled;
 
         return $composerInstaller;
     }
diff --git a/src/ComposerIntegration/VersionSelectorFactory.php b/src/ComposerIntegration/VersionSelectorFactory.php
index 60a6954..ef81ef6 100644
--- a/src/ComposerIntegration/VersionSelectorFactory.php
+++ b/src/ComposerIntegration/VersionSelectorFactory.php
@@ -35,7 +35,7 @@ public static function make(
     ): VersionSelector {
         return new VersionSelector(
             self::factoryRepositorySet($composer, $requestedPackageAndVersion->version),
-            new PhpBinaryPathBasedPlatformRepository($targetPlatform->phpBinaryPath),
+            new PhpBinaryPathBasedPlatformRepository($targetPlatform->phpBinaryPath, null),
         );
     }
 }
diff --git a/test/unit/ComposerIntegration/PhpBinaryPathBasedPlatformRepositoryTest.php b/test/unit/ComposerIntegration/PhpBinaryPathBasedPlatformRepositoryTest.php
index 72213d8..1fc7c65 100644
--- a/test/unit/ComposerIntegration/PhpBinaryPathBasedPlatformRepositoryTest.php
+++ b/test/unit/ComposerIntegration/PhpBinaryPathBasedPlatformRepositoryTest.php
@@ -6,6 +6,7 @@
 
 use Composer\Package\PackageInterface;
 use Php\Pie\ComposerIntegration\PhpBinaryPathBasedPlatformRepository;
+use Php\Pie\ExtensionName;
 use Php\Pie\Platform\TargetPhp\PhpBinaryPath;
 use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\TestCase;
@@ -30,7 +31,7 @@ public function testPlatformRepositoryContainsExpectedPacakges(): void
                 'another' => '1.2.3-alpha.34',
             ]);
 
-        $platformRepository = new PhpBinaryPathBasedPlatformRepository($phpBinaryPath);
+        $platformRepository = new PhpBinaryPathBasedPlatformRepository($phpBinaryPath, null);
 
         self::assertSame(
             [
@@ -46,4 +47,33 @@ public function testPlatformRepositoryContainsExpectedPacakges(): void
             ),
         );
     }
+
+    public function testPlatformRepositoryExcludesExtensionBeingInstalled(): void
+    {
+        $extensionBeingInstalled = ExtensionName::normaliseFromString('extension_being_installed');
+
+        $phpBinaryPath = $this->createMock(PhpBinaryPath::class);
+        $phpBinaryPath->expects(self::once())
+            ->method('version')
+            ->willReturn('8.1.0');
+        $phpBinaryPath->expects(self::once())
+            ->method('extensions')
+            ->willReturn([
+                'foo' => '8.1.0',
+                'extension_being_installed' => '1.2.3',
+            ]);
+
+        $platformRepository = new PhpBinaryPathBasedPlatformRepository($phpBinaryPath, $extensionBeingInstalled);
+
+        self::assertSame(
+            [
+                'php:8.1.0',
+                'ext-foo:8.1.0',
+            ],
+            array_map(
+                static fn (PackageInterface $package): string => $package->getName() . ':' . $package->getPrettyVersion(),
+                $platformRepository->getPackages(),
+            ),
+        );
+    }
 }