diff --git a/src/app/ui/timeline/timeline_observer.h b/src/app/ui/timeline/timeline_observer.h
new file mode 100644
index 000000000..df011a2c1
--- /dev/null
+++ b/src/app/ui/timeline/timeline_observer.h
@@ -0,0 +1,24 @@
+// Aseprite
+// Copyright (C) 2021  Igara Studio S.A.
+//
+// This program is distributed under the terms of
+// the End-User License Agreement for Aseprite.
+
+#ifndef APP_UI_TIMELINE_TIMELINE_OBSERVER_H_INCLUDED
+#define APP_UI_TIMELINE_TIMELINE_OBSERVER_H_INCLUDED
+#pragma once
+
+namespace app {
+  class Timeline;
+
+  class TimelineObserver {
+  public:
+    virtual ~TimelineObserver() { }
+
+    // Called when the current timeline range is going to change.
+    virtual void onBeforeRangeChanged(Timeline* timeline) { }
+  };
+
+} // namespace app
+
+#endif