diff --git a/Chapter_05/lib/recipe_book.dart b/Chapter_05/lib/recipe_book.dart
index 5d3e697..bf3c2d8 100644
--- a/Chapter_05/lib/recipe_book.dart
+++ b/Chapter_05/lib/recipe_book.dart
@@ -40,15 +40,15 @@ kitchen and took the recipe book with him!""";
   }
 
   // Tooltip
-  static final tooltip = new Expando<TooltipModel>();
+  static final _tooltip = new Expando<TooltipModel>();
   TooltipModel tooltipForRecipe(Recipe recipe) {
-    if (tooltip[recipe] == null) {
-      tooltip[recipe] = new TooltipModel(recipe.imgUrl,
+    if (_tooltip[recipe] == null) {
+      _tooltip[recipe] = new TooltipModel(recipe.imgUrl,
           "I don't have a picture of these recipes, "
           "so here's one of my cat instead!",
           80);
     }
-    return tooltip[recipe]; // recipe.tooltip
+    return _tooltip[recipe]; // recipe.tooltip
   }
 
   void clearFilters() {