diff --git a/src/wp-includes/class-wp-rewrite.php b/src/wp-includes/class-wp-rewrite.php
index 8b75fa5c36d16..5fd699f4420b5 100644
--- a/src/wp-includes/class-wp-rewrite.php
+++ b/src/wp-includes/class-wp-rewrite.php
@@ -1405,6 +1405,7 @@ public function rewrite_rules() {
 		$page_rewrite = apply_filters( 'page_rewrite_rules', $page_rewrite );
 
 		// Extra permastructs.
+		$permastruct_rewrite = array();
 		foreach ( $this->extra_permastructs as $permastructname => $struct ) {
 			if ( is_array( $struct ) ) {
 				if ( count( $struct ) === 2 ) {
@@ -1447,14 +1448,14 @@ public function rewrite_rules() {
 				$rules = apply_filters_deprecated( 'tag_rewrite_rules', array( $rules ), '3.1.0', 'post_tag_rewrite_rules' );
 			}
 
-			$this->extra_rules_top = array_merge( $this->extra_rules_top, $rules );
+			$permastruct_rewrite = array_merge( $permastruct_rewrite, $rules );
 		}
 
 		// Put them together.
 		if ( $this->use_verbose_page_rules ) {
-			$this->rules = array_merge( $this->extra_rules_top, $robots_rewrite, $favicon_rewrite, $sitemap_rewrite, $deprecated_files, $registration_pages, $root_rewrite, $comments_rewrite, $search_rewrite, $author_rewrite, $date_rewrite, $page_rewrite, $post_rewrite, $this->extra_rules );
+			$this->rules = array_merge( $this->extra_rules_top + $permastruct_rewrite, $robots_rewrite, $favicon_rewrite, $sitemap_rewrite, $deprecated_files, $registration_pages, $root_rewrite, $comments_rewrite, $search_rewrite, $author_rewrite, $date_rewrite, $page_rewrite, $post_rewrite, $this->extra_rules );
 		} else {
-			$this->rules = array_merge( $this->extra_rules_top, $robots_rewrite, $favicon_rewrite, $sitemap_rewrite, $deprecated_files, $registration_pages, $root_rewrite, $comments_rewrite, $search_rewrite, $author_rewrite, $date_rewrite, $post_rewrite, $page_rewrite, $this->extra_rules );
+			$this->rules = array_merge( $this->extra_rules_top + $permastruct_rewrite, $robots_rewrite, $favicon_rewrite, $sitemap_rewrite, $deprecated_files, $registration_pages, $root_rewrite, $comments_rewrite, $search_rewrite, $author_rewrite, $date_rewrite, $post_rewrite, $page_rewrite, $this->extra_rules );
 		}
 
 		/**
diff --git a/tests/phpunit/tests/rewrite.php b/tests/phpunit/tests/rewrite.php
index 2bb7254abfcef..badb06685c5bb 100644
--- a/tests/phpunit/tests/rewrite.php
+++ b/tests/phpunit/tests/rewrite.php
@@ -489,6 +489,82 @@ public function test_parse_request_with_post_slug_that_clashes_with_a_trashed_pa
 		$this->assertFalse( is_404() );
 	}
 
+	/**
+	 * @ticket 14991
+	 */
+	public function test_extra_rules_top_takes_priority_over_extra_permastructs() {
+		global $wp_rewrite;
+
+		// Register a custom permastruct with a known pattern.
+		add_permastruct(
+			'test_permastruct_14991',
+			'/test_permastruct_14991/%test_permastruct_14991%',
+			array(
+				'walk_dirs' => false,
+				'paged'     => false,
+				'feed'      => false,
+			)
+		);
+
+		$wp_rewrite->flush_rules();
+		$rewrite_rules = $wp_rewrite->rewrite_rules();
+
+		// Find a pattern generated by the permastruct.
+		$permastruct_pattern = null;
+		foreach ( array_keys( $rewrite_rules ) as $pattern ) {
+			if ( str_contains( $pattern, 'test_permastruct_14991' ) ) {
+				$permastruct_pattern = $pattern;
+				break;
+			}
+		}
+
+		$this->assertNotNull( $permastruct_pattern, 'Expected a rewrite rule to be generated for the permastruct.' );
+
+		// Add a top-priority rule with the same regex pattern.
+		$top_query = 'index.php?custom_override=1';
+		$wp_rewrite->add_rule( $permastruct_pattern, $top_query, 'top' );
+
+		$wp_rewrite->flush_rules();
+		$rewrite_rules = $wp_rewrite->rewrite_rules();
+
+		// The top rule's query should win over the permastruct's.
+		$this->assertSame(
+			$top_query,
+			$rewrite_rules[ $permastruct_pattern ],
+			'extra_rules_top should take priority over extra_permastructs when there is a regex conflict.'
+		);
+	}
+
+	/**
+	 * @ticket 14991
+	 */
+	public function test_extra_rules_top_is_not_polluted_by_permastruct_rules() {
+		global $wp_rewrite;
+
+		// Register a custom permastruct.
+		add_permastruct(
+			'test_permastruct_14991_c',
+			'/test_permastruct_14991_c/%test_permastruct_14991_c%',
+			array(
+				'walk_dirs' => false,
+				'paged'     => false,
+				'feed'      => false,
+			)
+		);
+
+		$wp_rewrite->flush_rules();
+		$wp_rewrite->rewrite_rules();
+
+		// $extra_rules_top should only contain manually-added rules, not permastruct-generated ones.
+		foreach ( array_keys( $wp_rewrite->extra_rules_top ) as $pattern ) {
+			$this->assertStringNotContainsString(
+				'test_permastruct_14991_c',
+				$pattern,
+				'Permastruct-generated rules must not be stored in $extra_rules_top.'
+			);
+		}
+	}
+
 	/**
 	 * @ticket 29107
 	 */