diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0578a3f0..4d6c757f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 - Fixed a bug where custom `toolbar` config settings were getting ignored. ([#522](https://github.com/craftcms/ckeditor/issues/522))
 - Fixed a bug where files uploaded to Assets fields could also be added to nearby CKEditor fields. ([#523](https://github.com/craftcms/ckeditor/issues/523))
+- Fixed an error that could occur when registering a custom CKEditor plugin. ([#525](https://github.com/craftcms/ckeditor/issues/525))
 
 ## 5.1.0 - 2026-03-05
 
diff --git a/src/helpers/CkeditorConfig.php b/src/helpers/CkeditorConfig.php
index b739b586..6e25b1f2 100644
--- a/src/helpers/CkeditorConfig.php
+++ b/src/helpers/CkeditorConfig.php
@@ -214,12 +214,7 @@ public static function registerPackage(string $name, array $config): void
         $plugins = $config['plugins'] ?? [];
         $toolbarItems = $config['toolbarItems'] ?? [];
 
-        if (!isset(self::$pluginsByPackage[$name])) {
-            self::$pluginsByPackage[$name] = $plugins;
-        } else {
-            self::$pluginsByPackage[$name] = array_merge(self::$pluginsByPackage[$name], $plugins);
-        }
-
+        self::$pluginsByPackage[$name] = $plugins;
         self::$toolbarItems[] = $toolbarItems;
         self::$pluginButtonMap[] = [
             'plugins' => $plugins,