diff --git a/lib/src/common/observer_controller.dart b/lib/src/common/observer_controller.dart
index c4a0b7f..4b57bf3 100644
--- a/lib/src/common/observer_controller.dart
+++ b/lib/src/common/observer_controller.dart
@@ -210,7 +210,11 @@ mixin ObserverControllerForInfo on ObserverController {
 
   /// Getting [maxScrollExtent] of viewport
   double viewportMaxScrollExtent(RenderViewportBase viewport) {
-    return (viewport.offset as ScrollPositionWithSingleContext).maxScrollExtent;
+    final offset = viewport.offset;
+    if (offset is! ScrollPosition) {
+      return 0;
+    }
+    return offset.maxScrollExtent;
   }
 }