diff --git a/Tween.h b/Tween.h
index dca02e2..20512c4 100644
--- a/Tween.h
+++ b/Tween.h
@@ -84,7 +84,7 @@ public:
     isPlayingF = false;
   }
 
-  bool isPlaying() {
+  bool isPlaying() const {
     return isPlayingF;
   }