diff --git a/source/script.php b/source/script.php
index a0c155ee..0e772ebf 100644
--- a/source/script.php
+++ b/source/script.php
@@ -511,7 +511,22 @@ class Pkg_MokosuiteclientInstallerScript
 				return;
 			}
 
-			// No row exists at all — create one from the manifest XML on disk
+			// Verify no row exists before inserting (prevent duplicates)
+			$db->setQuery(
+				$db->getQuery(true)
+					->select('COUNT(*)')
+					->from($db->quoteName('#__extensions'))
+					->where($db->quoteName('type') . ' = ' . $db->quote('plugin'))
+					->where($db->quoteName('folder') . ' = ' . $db->quote($group))
+					->where($db->quoteName('element') . ' = ' . $db->quote($element))
+			);
+
+			if ((int) $db->loadResult() > 0)
+			{
+				return;
+			}
+
+			// No row exists — create one from the manifest XML on disk
 			$manifestFile = $pluginDir . '/' . $element . '.xml';
 
 			if (is_file($manifestFile))
@@ -577,7 +592,7 @@ class Pkg_MokosuiteclientInstallerScript
 			$db->execute();
 			$deleted = $db->getAffectedRows();
 
-			// Also delete rows where element is the display name (spaces)
+			// Delete rows where element is the display name (spaces)
 			$db->setQuery(
 				$db->getQuery(true)
 					->delete($db->quoteName('#__extensions'))
@@ -592,6 +607,22 @@ class Pkg_MokosuiteclientInstallerScript
 				Log::add("Deleted {$deleted} orphaned plugin row(s)", Log::INFO, 'mokosuiteclient');
 			}
 
+			// Deduplicate: keep only the lowest extension_id per element+folder
+			$db->setQuery(
+				"DELETE e1 FROM " . $db->quoteName('#__extensions') . " e1"
+				. " INNER JOIN " . $db->quoteName('#__extensions') . " e2"
+				. " ON e1.element = e2.element AND e1.folder = e2.folder AND e1.type = e2.type"
+				. " AND e1.extension_id > e2.extension_id"
+				. " WHERE e1.element LIKE 'mokosuiteclient%' AND e1.type = 'plugin'"
+			);
+			$db->execute();
+			$deduped = $db->getAffectedRows();
+
+			if ($deduped > 0)
+			{
+				Log::add("Removed {$deduped} duplicate extension row(s)", Log::INFO, 'mokosuiteclient');
+			}
+
 			// 2. Clean up stale plugin files that leaked to group roots
 			$groupDirs = [JPATH_PLUGINS . '/system', JPATH_PLUGINS . '/task', JPATH_PLUGINS . '/webservices'];