diff --git a/wp-includes/comment.php b/wp-includes/comment.php
index d8ca7859da..225e786b43 100644
--- a/wp-includes/comment.php
+++ b/wp-includes/comment.php
@@ -1290,7 +1290,12 @@ function wp_insert_comment($commentdata) {
 	$comment = get_comment($id);
 	do_action('wp_insert_comment', $id, $comment);
 
-	wp_cache_incr( 'last_changed', 1, 'comment' );
+	if ( function_exists( 'wp_cache_incr' ) ) {
+		wp_cache_incr( 'last_changed', 1, 'comment' );
+	} else {
+		$last_changed = wp_cache_get( 'last_changed', 'comment' );
+		wp_cache_set( 'last_changed', $last_changed + 1, 'comment' );
+	}
 
 	return $id;
 }
@@ -1963,7 +1968,12 @@ function clean_comment_cache($ids) {
 	foreach ( (array) $ids as $id )
 		wp_cache_delete($id, 'comment');
 
-	wp_cache_incr( 'last_changed', 1, 'comment' );
+	if ( function_exists( 'wp_cache_incr' ) ) {
+		wp_cache_incr( 'last_changed', 1, 'comment' );
+	} else {
+		$last_changed = wp_cache_get( 'last_changed', 'comment' );
+		wp_cache_set( 'last_changed', $last_changed + 1, 'comment' );
+	}
 }
 
 /**