diff --git a/system/Autoloader/Autoloader.php b/system/Autoloader/Autoloader.php
index 4666149f27e9..1d28cfc4c018 100644
--- a/system/Autoloader/Autoloader.php
+++ b/system/Autoloader/Autoloader.php
@@ -418,7 +418,9 @@ private function loadComposerNamespaces(ClassLoader $composer, array $composerPa
         $packageList = [];
 
         foreach ($allData as $list) {
-            $packageList = array_merge($packageList, $list['versions']);
+            foreach ($list['versions'] as $packageName => $data) {
+                $packageList[$packageName] = $data;
+            }
         }
 
         // Check config for $composerPackages.
diff --git a/tests/system/Autoloader/AutoloaderTest.php b/tests/system/Autoloader/AutoloaderTest.php
index be22e4a403f1..8e1d81cd1c14 100644
--- a/tests/system/Autoloader/AutoloaderTest.php
+++ b/tests/system/Autoloader/AutoloaderTest.php
@@ -20,6 +20,7 @@
 use CodeIgniter\Exceptions\RuntimeException;
 use CodeIgniter\Test\CIUnitTestCase;
 use CodeIgniter\Test\ReflectionHelper;
+use Composer\Autoload\ClassLoader;
 use Config\Autoload;
 use Config\Modules;
 use PHPUnit\Framework\Attributes\Group;
@@ -417,6 +418,22 @@ public function testFindsComposerRoutesWithComposerPathNotFound(): void
         $this->assertArrayNotHasKey('Laminas\\Escaper', $namespaces);
     }
 
+    public function testLoadComposerNamespacesAccumulatesCorrectly(): void
+    {
+        $composer = $this->createMock(ClassLoader::class);
+        $composer->method('getPrefixesPsr4')->willReturn([
+            'Laminas\\Escaper\\' => [VENDORPATH . 'composer/../laminas/laminas-escaper/src'],
+        ]);
+
+        $loader  = new Autoloader();
+        $invoker = self::getPrivateMethodInvoker($loader, 'loadComposerNamespaces');
+
+        $invoker($composer, []);
+
+        $namespaces = $loader->getNamespace();
+        $this->assertArrayHasKey('Laminas\\Escaper', $namespaces);
+    }
+
     public function testAutoloaderLoadsNonClassFiles(): void
     {
         $config          = new Autoload();