diff --git a/src/js/plyr.js b/src/js/plyr.js
index eb7b9f2d..a676f635 100644
--- a/src/js/plyr.js
+++ b/src/js/plyr.js
@@ -1983,6 +1983,10 @@
 
         // Speed-up
         function _speedup(speed) {
+            if (!_is.array(config.speeds)) {
+                _warn('Invalid speeds format');
+                return;
+            }
             if (!_is.number(speed)) {
                 var index = config.speeds.indexOf(config.currentSpeed);
                 if (index !== -1) {