diff --git a/src/psm/Util/Server/HistoryGraph.class.php b/src/psm/Util/Server/HistoryGraph.class.php
index 53b900fa..2ee728ad 100644
--- a/src/psm/Util/Server/HistoryGraph.class.php
+++ b/src/psm/Util/Server/HistoryGraph.class.php
@@ -184,7 +184,7 @@ class HistoryGraph {
 	 * @param boolean $add_uptime add uptime calculation?
 	 * @return array
 	 */
-	protected function generateGraphLines($records, $lines, callable $cb_if_up, $latency_avg_key, $add_uptime = false) {
+	protected function generateGraphLines($records, $lines, $cb_if_up, $latency_avg_key, $add_uptime = false) {
 		$data = array();
 
 		// PLEASE NOTE: all times are in microseconds! because of javascript.
@@ -263,4 +263,4 @@ class HistoryGraph {
 
 		return $data;
 	}
-}
\ No newline at end of file
+}