diff --git a/src/StaticPHP/Command/Dev/GenExtTestMatrixCommand.php b/src/StaticPHP/Command/Dev/GenExtTestMatrixCommand.php
index 44816863..674c8075 100644
--- a/src/StaticPHP/Command/Dev/GenExtTestMatrixCommand.php
+++ b/src/StaticPHP/Command/Dev/GenExtTestMatrixCommand.php
@@ -107,7 +107,12 @@ class GenExtTestMatrixCommand extends BaseCommand
         // Separate into regular and virtual extensions (build-static:false excluded globally)
         $all_regular = [];
         $all_virtual = [];
+        $all_libraries = [];
         foreach ($all as $pkg_name => $config) {
+            if (($config['type'] ?? '') === 'library') {
+                $all_libraries[$pkg_name] = $config;
+                continue;
+            }
             if (($config['type'] ?? '') !== 'php-extension') {
                 continue;
             }
@@ -154,10 +159,7 @@ class GenExtTestMatrixCommand extends BaseCommand
                     $raw,
                     fn ($d) => isset($pool_set[$d]) && $d !== $pkg_name
                 ));
-                $os_lib_deps[$this->displayName($pkg_name)] = array_values(array_filter(
-                    $raw,
-                    fn ($d) => !str_starts_with($d, 'ext-')
-                ));
+                $os_lib_deps[$this->displayName($pkg_name)] = $this->collectLibraryDeps($raw, $all_libraries, $os);
             }
             $all_ext_lib_deps[$os] = $os_lib_deps;
 
@@ -300,6 +302,41 @@ class GenExtTestMatrixCommand extends BaseCommand
         return str_starts_with($pkg_name, 'ext-') ? substr($pkg_name, 4) : $pkg_name;
     }
 
+    /**
+     * Collect direct and transitive library dependencies from a package dependency list.
+     *
+     * @param string[]               $deps
+     * @param array<string, mixed[]> $library_configs
+     * @param array<string, true>    $seen
+     *
+     * @return string[]
+     */
+    private function collectLibraryDeps(array $deps, array $library_configs, string $platform, array $seen = []): array
+    {
+        $collected = [];
+        foreach ($deps as $dep) {
+            if (str_starts_with($dep, 'ext-') || isset($seen[$dep])) {
+                continue;
+            }
+
+            $seen[$dep] = true;
+            $collected[$dep] = $dep;
+
+            if (!isset($library_configs[$dep])) {
+                continue;
+            }
+
+            $child_deps = array_merge(
+                $this->resolvePlatformList($library_configs[$dep], 'depends', $platform),
+                $this->resolvePlatformList($library_configs[$dep], 'suggests', $platform),
+            );
+            foreach ($this->collectLibraryDeps($child_deps, $library_configs, $platform, $seen) as $child_dep) {
+                $collected[$child_dep] = $child_dep;
+            }
+        }
+        return array_values($collected);
+    }
+
     /**
      * Split orphans into batches such that no two conflicting extensions share a batch.
      * Uses a greedy graph-coloring approach.
diff --git a/tests/StaticPHP/Command/Dev/GenExtTestMatrixCommandTest.php b/tests/StaticPHP/Command/Dev/GenExtTestMatrixCommandTest.php
index b6beb6fb..4e3fc33a 100644
--- a/tests/StaticPHP/Command/Dev/GenExtTestMatrixCommandTest.php
+++ b/tests/StaticPHP/Command/Dev/GenExtTestMatrixCommandTest.php
@@ -176,6 +176,20 @@ class GenExtTestMatrixCommandTest extends TestCase
         }
     }
 
+    /**
+     * --for-libs must include extensions that depend on the library through other libraries.
+     */
+    public function testForLibsFilterIncludesTransitiveLibraryDeps(): void
+    {
+        $matrix = $this->runMatrix(['--os' => 'Linux', '--for-libs' => 'libde265']);
+
+        $this->assertNotEmpty($matrix, '--for-libs=libde265 must yield at least one entry');
+        foreach ($matrix as $entry) {
+            $parts = explode(',', $entry['extension']);
+            $this->assertContains('imagick', $parts, "Entry {$entry['extension']} should not appear in --for-libs=libde265 results");
+        }
+    }
+
     /**
      * --tier2 must produce only Tier2 runners and no Windows entries.
      */
@@ -260,12 +274,14 @@ class GenExtTestMatrixCommandTest extends TestCase
      *  - ext-redis           simple orphan
      *  - ext-xml             depends on lib 'libxml2'
      *  - ext-dom             depends on ext-xml (DFS chain)
+     *  - ext-imagick         depends on imagemagick -> libheif -> libde265
      *  - ext-linux-only      restricted to Linux via os: [Linux]
      */
     private static function buildFixture(): array
     {
         // php-extension must be a non-empty assoc array ([] fails is_assoc_array() check).
         $ext = static fn (array $phpExt = ['arg-type' => 'standard'], array $topLevel = []): array => array_merge(['type' => 'php-extension', 'php-extension' => $phpExt], $topLevel);
+        $lib = static fn (array $topLevel = []): array => array_merge(['type' => 'library', 'artifact' => ['source' => 'custom']], $topLevel);
 
         return [
             // Isolated standalones
@@ -284,6 +300,12 @@ class GenExtTestMatrixCommandTest extends TestCase
             'ext-xml' => $ext(['arg-type' => 'standard'], ['depends' => ['libxml2']]),
             'ext-dom' => $ext(['arg-type' => 'standard'], ['depends' => ['ext-xml']]),
 
+            // Transitive library chain: imagick -> imagemagick -> libheif -> libde265
+            'ext-imagick' => $ext(['arg-type' => 'standard'], ['depends' => ['imagemagick']]),
+            'imagemagick' => $lib(['depends' => ['libheif']]),
+            'libheif' => $lib(['depends' => ['libde265']]),
+            'libde265' => $lib(),
+
             // OS-restricted to Linux only
             'ext-linux-only' => $ext(['os' => ['Linux']]),
         ];