diff --git a/extension.json b/extension.json
index 108ea60..63330b6 100644
--- a/extension.json
+++ b/extension.json
@@ -18,8 +18,7 @@
 		"MediaWiki\\PrevNextImageLinks\\AssociatedImage": "includes/AssociatedImage.php",
 		"MediaWiki\\PrevNextImageLinks\\Hooks": "includes/Hooks.php",
 		"MediaWiki\\PrevNextImageLinks\\NavigationTemplate": "includes/NavigationTemplate.php",
-		"MediaWiki\\PrevNextImageLinks\\PageFinder": "includes/PageFinder.php",
-		"MediaWiki\\PrevNextImageLinks\\RomanNumeral": "includes/util/RomanNumeral.php"
+		"MediaWiki\\PrevNextImageLinks\\PageFinder": "includes/PageFinder.php"
 	},
 	"ExtensionMessagesFiles": {
 		"PrevNextImageLinksMagic": "PrevNextImageLinks.i18n.magic.php"
diff --git a/includes/NavigationTemplate.php b/includes/NavigationTemplate.php
index b69db91..fb166ab 100644
--- a/includes/NavigationTemplate.php
+++ b/includes/NavigationTemplate.php
@@ -49,7 +49,8 @@ public static function pfSubpageAnchorNavigation( Parser $parser, $pageName ) {
 
 	/**
 	 * Find all subpages of $title, find all tags like <span id="pg123"> inside each subpage,
-	 * then generate links to every #pg<number> anchor, sorted by number after "pg".
+	 * then generate links to every #pg<number> anchor,
+	 * sorted by first parameter of {{#set_associated_index:}} that is associated with this anchor.
 	 * @param PageIdentity $title
 	 * @return string|array
 	 */
@@ -59,7 +60,11 @@ protected function generate( PageIdentity $title ) {
 
 		// Find all subpages of $title.
 		$res = $dbr->newSelectQueryBuilder()
-			->select( [ 'page_title AS title', 'pp_value AS anchor' ] )
+			->select( [
+				'page_title AS title',
+				'pp_value AS anchor',
+				'pp_propname AS sortkey'
+			] )
 			->from( 'page' )
 			->join( 'page_props', null, [ 'pp_page = page_id' ] )
 			->where( [
@@ -80,29 +85,29 @@ protected function generate( PageIdentity $title ) {
 		foreach ( $res as $row ) {
 			// Strip standard prefix ("pg").
 			$shownAnchor = preg_replace( '/^pg/', '', $row->anchor );
-			$number = $this->parseAnchorNumber( $row->anchor );
-			if ( $number < 0 ) {
-				// Negative numbers (e.g. "pg-5") are NOT shown in the navigation template.
+			if ( !$shownAnchor || $shownAnchor[0] === '-' ) {
+				// Empty anchors and anchors with negative numbers (e.g. "pg-5")
+				// are NOT shown in the navigation template.
 				continue;
 			}
 
+			$sortkey = intval( preg_replace( '/^associatedPageIndex\./', '', $row->sortkey ) );
+
 			$anchorsFound[] = [
 				'title' => $row->title,
 				'anchor' => $row->anchor,
 				'text' => $shownAnchor,
-				'number' => $number
+				'sortkey' => $sortkey
 			];
 		}
 
 		uasort( $anchorsFound, static function ( $a, $b ) {
-			// Sort by number.
-			$cmp = $a['number'] - $b['number'];
+			$cmp = $a['sortkey'] - $b['sortkey'];
 			if ( $cmp !== 0 ) {
 				return $cmp;
 			}
 
-			// If numbers are the same (likely non-numeric anchors?),
-			// then sort by displayed text.
+			// If sortkeys are the same, then sort by displayed text.
 			return strcmp( $a['text'], $b['text'] );
 		} );
 
@@ -119,25 +124,4 @@ protected function generate( PageIdentity $title ) {
 		);
 		return [ $resultHtml, 'isHTML' => true ];
 	}
-
-	/**
-	 * Detect the number inside the string $anchor, e.g. "15" in "pg15" or "9" in "pg-ix".
-	 * @param string $anchor
-	 * @return int
-	 */
-	protected function parseAnchorNumber( $anchor ) {
-		// Decimal number?
-		if ( preg_match( '/\-?[0-9]+/', $anchor, $matches ) ) {
-			return (int)$matches[0];
-		}
-
-		$value = RomanNumeral::romanToInteger( $anchor );
-		if ( $value ) {
-			// Found and successfully parsed roman numeral.
-			return $value;
-		}
-
-		// Default (no number found). These anchors can still be shown.
-		return 0;
-	}
 }
diff --git a/includes/util/RomanNumeral.php b/includes/util/RomanNumeral.php
deleted file mode 100644
index 768e5dd..0000000
--- a/includes/util/RomanNumeral.php
+++ /dev/null
@@ -1,36 +0,0 @@
-<?php
-
-/**
- * Implements SubpageAnchorNavigation extension for MediaWiki.
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along
- * with this program; if not, write to the Free Software Foundation, Inc.,
- * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
- * http://www.gnu.org/copyleft/gpl.html
- *
- * @file
- */
-
-namespace MediaWiki\PrevNextImageLinks;
-
-class RomanNumeral {
-	/**
-	 * Convert roman numeral into integer.
-	 * @param string $roman
-	 * @return int Resulting number (if converted successfully) or 0 if $roman is not a valid numeral.
-	 */
-	public static function romanToInteger( $roman ) {
-		// TODO.
-		return 0;
-	}
-}