diff --git a/libraries.services.yml b/libraries.services.yml
index 6da6e3a68b4e71d6acec2414665a2871011a94f6..ffa6bbb73915130d97cb3273c72a526205599c51 100644
--- a/libraries.services.yml
+++ b/libraries.services.yml
@@ -7,8 +7,7 @@ services:
       - '@libraries.php_file_loader'
   libraries.registry:
     class: Drupal\libraries\ExternalLibrary\Registry\ExternalLibraryRegistry
-    # @todo Reconsider the decision to go with JSON instead of YAML.
-    arguments: ['@serialization.json', '@plugin.manager.libraries.locator']
+    arguments: ['@serialization.yaml', '@plugin.manager.libraries.locator']
   plugin.manager.libraries.locator:
     class: Drupal\libraries\ExternalLibrary\Local\LocatorManager
     parent: default_plugin_manager
diff --git a/tests/library_definitions/test_asset_library.json b/tests/library_definitions/test_asset_library.json
deleted file mode 100644
index da7eeee4dcd1d8ad6e10014d03e225e343aa52c3..0000000000000000000000000000000000000000
--- a/tests/library_definitions/test_asset_library.json
+++ /dev/null
@@ -1,13 +0,0 @@
-{
-  "id": "test_asset_library",
-  "class": "Drupal\\libraries\\ExternalLibrary\\Asset\\AssetLibrary",
-  "remote_url": "http://example.com",
-  "css": {
-    "base": {
-      "example.css": []
-    }
-  },
-  "js": {
-    "example.js": []
-  }
-}
diff --git a/tests/library_definitions/test_asset_library.yml b/tests/library_definitions/test_asset_library.yml
new file mode 100644
index 0000000000000000000000000000000000000000..e00036eaed1901922ba14aec406fca81b2dc4040
--- /dev/null
+++ b/tests/library_definitions/test_asset_library.yml
@@ -0,0 +1,8 @@
+id: test_asset_library
+class: Drupal\libraries\ExternalLibrary\Asset\AssetLibrary
+remote_url: http://example.com
+css:
+  base:
+    example.css: {  }
+js:
+  example.js: {  }
diff --git a/tests/library_definitions/test_php_file_library.json b/tests/library_definitions/test_php_file_library.json
deleted file mode 100644
index 7301a04080b20776f3583a58569ca202c459bb4a..0000000000000000000000000000000000000000
--- a/tests/library_definitions/test_php_file_library.json
+++ /dev/null
@@ -1,7 +0,0 @@
-{
-  "id": "test_php_file_library",
-  "class": "Drupal\\libraries\\ExternalLibrary\\PhpFile\\PhpFileLibrary",
-  "files": [
-    "test_php_file_library.php"
-  ]
-}
diff --git a/tests/library_definitions/test_php_file_library.yml b/tests/library_definitions/test_php_file_library.yml
new file mode 100644
index 0000000000000000000000000000000000000000..4d1e423bb71530787d09bd08c2a26f1ae9f8f36b
--- /dev/null
+++ b/tests/library_definitions/test_php_file_library.yml
@@ -0,0 +1,3 @@
+id: test_php_file_library
+class: Drupal\libraries\ExternalLibrary\PhpFile\PhpFileLibrary
+files: [test_php_file_library.php]