diff --git a/packages/flutter/lib/src/cupertino/action_sheet.dart b/packages/flutter/lib/src/cupertino/action_sheet.dart
index 4e49dce71b..c5fa8d06a3 100644
--- a/packages/flutter/lib/src/cupertino/action_sheet.dart
+++ b/packages/flutter/lib/src/cupertino/action_sheet.dart
@@ -489,7 +489,7 @@ class _CupertinoAlertRenderElement extends RenderObjectElement {
   }
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     super.mount(parent, newSlot);
     _contentElement = updateChild(_contentElement,
         widget.contentSection, _AlertSections.contentSection);
diff --git a/packages/flutter/lib/src/cupertino/dialog.dart b/packages/flutter/lib/src/cupertino/dialog.dart
index da3973a711..8203d66b0d 100644
--- a/packages/flutter/lib/src/cupertino/dialog.dart
+++ b/packages/flutter/lib/src/cupertino/dialog.dart
@@ -389,7 +389,7 @@ class _CupertinoDialogRenderElement extends RenderObjectElement {
   }
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     super.mount(parent, newSlot);
     _contentElement = updateChild(_contentElement, widget.contentSection, _AlertDialogSections.contentSection);
     _actionsElement = updateChild(_actionsElement, widget.actionsSection, _AlertDialogSections.actionsSection);
diff --git a/packages/flutter/lib/src/cupertino/text_selection_toolbar.dart b/packages/flutter/lib/src/cupertino/text_selection_toolbar.dart
index 2f76b403b0..620ccd4c9a 100644
--- a/packages/flutter/lib/src/cupertino/text_selection_toolbar.dart
+++ b/packages/flutter/lib/src/cupertino/text_selection_toolbar.dart
@@ -535,7 +535,7 @@ class _CupertinoTextSelectionToolbarItemsElement extends RenderObjectElement {
   }
 
   @override
-  void insertRenderObjectChild(RenderObject child, dynamic slot) {
+  void insertRenderObjectChild(RenderObject child, Object? slot) {
     if (slot is _CupertinoTextSelectionToolbarItemsSlot) {
       assert(child is RenderBox);
       _updateRenderObject(child as RenderBox, slot);
@@ -562,7 +562,7 @@ class _CupertinoTextSelectionToolbarItemsElement extends RenderObjectElement {
   }
 
   @override
-  void removeRenderObjectChild(RenderObject child, dynamic slot) {
+  void removeRenderObjectChild(RenderObject child, Object? slot) {
     // Check if the child is in a slot.
     if (slot is _CupertinoTextSelectionToolbarItemsSlot) {
       assert(child is RenderBox);
@@ -614,7 +614,7 @@ class _CupertinoTextSelectionToolbarItemsElement extends RenderObjectElement {
   }
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     super.mount(parent, newSlot);
     // Mount slotted children.
     _mountChild(widget.backButton, _CupertinoTextSelectionToolbarItemsSlot.backButton);
diff --git a/packages/flutter/lib/src/material/chip.dart b/packages/flutter/lib/src/material/chip.dart
index 6422726f8d..0dcbc21fef 100644
--- a/packages/flutter/lib/src/material/chip.dart
+++ b/packages/flutter/lib/src/material/chip.dart
@@ -2189,7 +2189,7 @@ class _RenderChipElement extends RenderObjectElement {
   }
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     super.mount(parent, newSlot);
     _mountChild(widget.theme.avatar, _ChipSlot.avatar);
     _mountChild(widget.theme.deleteIcon, _ChipSlot.deleteIcon);
@@ -2246,7 +2246,7 @@ class _RenderChipElement extends RenderObjectElement {
   }
 
   @override
-  void moveRenderObjectChild(RenderObject child, dynamic oldSlot, dynamic newSlot) {
+  void moveRenderObjectChild(RenderObject child, Object? oldSlot, Object? newSlot) {
     assert(false, 'not reachable');
   }
 }
diff --git a/packages/flutter/lib/src/material/input_decorator.dart b/packages/flutter/lib/src/material/input_decorator.dart
index 9d1ef43006..a5d405ed28 100644
--- a/packages/flutter/lib/src/material/input_decorator.dart
+++ b/packages/flutter/lib/src/material/input_decorator.dart
@@ -1588,7 +1588,7 @@ class _DecorationElement extends RenderObjectElement {
   }
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     super.mount(parent, newSlot);
     _mountChild(widget.decoration.icon, _DecorationSlot.icon);
     _mountChild(widget.decoration.input, _DecorationSlot.input);
@@ -1685,7 +1685,7 @@ class _DecorationElement extends RenderObjectElement {
   }
 
   @override
-  void moveRenderObjectChild(RenderObject child, dynamic oldSlot, dynamic newSlot) {
+  void moveRenderObjectChild(RenderObject child, Object? oldSlot, Object? newSlot) {
     assert(false, 'not reachable');
   }
 }
diff --git a/packages/flutter/lib/src/material/list_tile.dart b/packages/flutter/lib/src/material/list_tile.dart
index 40744ad13c..254c1da99b 100644
--- a/packages/flutter/lib/src/material/list_tile.dart
+++ b/packages/flutter/lib/src/material/list_tile.dart
@@ -1327,7 +1327,7 @@ class _ListTileElement extends RenderObjectElement {
   }
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     super.mount(parent, newSlot);
     _mountChild(widget.leading, _ListTileSlot.leading);
     _mountChild(widget.title, _ListTileSlot.title);
@@ -1389,7 +1389,7 @@ class _ListTileElement extends RenderObjectElement {
   }
 
   @override
-  void moveRenderObjectChild(RenderObject child, dynamic oldSlot, dynamic newSlot) {
+  void moveRenderObjectChild(RenderObject child, Object? oldSlot, Object? newSlot) {
     assert(false, 'not reachable');
   }
 }
diff --git a/packages/flutter/lib/src/widgets/binding.dart b/packages/flutter/lib/src/widgets/binding.dart
index 35ecbc168b..28e4e91f75 100644
--- a/packages/flutter/lib/src/widgets/binding.dart
+++ b/packages/flutter/lib/src/widgets/binding.dart
@@ -1153,7 +1153,7 @@ class RenderObjectToWidgetElement<T extends RenderObject> extends RootRenderObje
   }
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     assert(parent == null);
     super.mount(parent, newSlot);
     _rebuild();
@@ -1204,19 +1204,19 @@ class RenderObjectToWidgetElement<T extends RenderObject> extends RootRenderObje
   RenderObjectWithChildMixin<T> get renderObject => super.renderObject as RenderObjectWithChildMixin<T>;
 
   @override
-  void insertRenderObjectChild(RenderObject child, dynamic slot) {
+  void insertRenderObjectChild(RenderObject child, Object? slot) {
     assert(slot == _rootChildSlot);
     assert(renderObject.debugValidateChild(child));
     renderObject.child = child as T;
   }
 
   @override
-  void moveRenderObjectChild(RenderObject child, dynamic oldSlot, dynamic newSlot) {
+  void moveRenderObjectChild(RenderObject child, Object? oldSlot, Object? newSlot) {
     assert(false);
   }
 
   @override
-  void removeRenderObjectChild(RenderObject child, dynamic slot) {
+  void removeRenderObjectChild(RenderObject child, Object? slot) {
     assert(renderObject.child == child);
     renderObject.child = null;
   }
diff --git a/packages/flutter/lib/src/widgets/layout_builder.dart b/packages/flutter/lib/src/widgets/layout_builder.dart
index 1fb4b1ae7d..80767fa122 100644
--- a/packages/flutter/lib/src/widgets/layout_builder.dart
+++ b/packages/flutter/lib/src/widgets/layout_builder.dart
@@ -79,7 +79,7 @@ class _LayoutBuilderElement<ConstraintType extends Constraints> extends RenderOb
   }
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     super.mount(parent, newSlot); // Creates the renderObject.
     renderObject.updateCallback(_layout);
   }
@@ -152,7 +152,7 @@ class _LayoutBuilderElement<ConstraintType extends Constraints> extends RenderOb
   }
 
   @override
-  void insertRenderObjectChild(RenderObject child, dynamic slot) {
+  void insertRenderObjectChild(RenderObject child, Object? slot) {
     final RenderObjectWithChildMixin<RenderObject> renderObject = this.renderObject;
     assert(slot == null);
     assert(renderObject.debugValidateChild(child));
@@ -161,12 +161,12 @@ class _LayoutBuilderElement<ConstraintType extends Constraints> extends RenderOb
   }
 
   @override
-  void moveRenderObjectChild(RenderObject child, dynamic oldSlot, dynamic newSlot) {
+  void moveRenderObjectChild(RenderObject child, Object? oldSlot, Object? newSlot) {
     assert(false);
   }
 
   @override
-  void removeRenderObjectChild(RenderObject child, dynamic slot) {
+  void removeRenderObjectChild(RenderObject child, Object? slot) {
     final RenderConstrainedLayoutBuilder<ConstraintType, RenderObject> renderObject = this.renderObject;
     assert(renderObject.child == child);
     renderObject.child = null;
diff --git a/packages/flutter/lib/src/widgets/list_wheel_scroll_view.dart b/packages/flutter/lib/src/widgets/list_wheel_scroll_view.dart
index f0c3e141bd..74adae5eb7 100644
--- a/packages/flutter/lib/src/widgets/list_wheel_scroll_view.dart
+++ b/packages/flutter/lib/src/widgets/list_wheel_scroll_view.dart
@@ -889,12 +889,12 @@ class ListWheelElement extends RenderObjectElement implements ListWheelChildMana
   }
 
   @override
-  Element? updateChild(Element? child, Widget? newWidget, dynamic newSlot) {
+  Element? updateChild(Element? child, Widget? newWidget, Object? newSlot) {
     final ListWheelParentData? oldParentData = child?.renderObject?.parentData as ListWheelParentData?;
     final Element? newChild = super.updateChild(child, newWidget, newSlot);
     final ListWheelParentData? newParentData = newChild?.renderObject?.parentData as ListWheelParentData?;
     if (newParentData != null) {
-      newParentData.index = newSlot as int;
+      newParentData.index = newSlot! as int;
       if (oldParentData != null)
         newParentData.offset = oldParentData.offset;
     }
diff --git a/packages/flutter/lib/src/widgets/sliver.dart b/packages/flutter/lib/src/widgets/sliver.dart
index 97cd54f4af..147e1cc5e3 100644
--- a/packages/flutter/lib/src/widgets/sliver.dart
+++ b/packages/flutter/lib/src/widgets/sliver.dart
@@ -1236,7 +1236,7 @@ class SliverMultiBoxAdaptorElement extends RenderObjectElement implements Render
   }
 
   @override
-  Element? updateChild(Element? child, Widget? newWidget, dynamic newSlot) {
+  Element? updateChild(Element? child, Widget? newWidget, Object? newSlot) {
     final SliverMultiBoxAdaptorParentData? oldParentData = child?.renderObject?.parentData as SliverMultiBoxAdaptorParentData?;
     final Element? newChild = super.updateChild(child, newWidget, newSlot);
     final SliverMultiBoxAdaptorParentData? newParentData = newChild?.renderObject?.parentData as SliverMultiBoxAdaptorParentData?;
diff --git a/packages/flutter/lib/src/widgets/sliver_persistent_header.dart b/packages/flutter/lib/src/widgets/sliver_persistent_header.dart
index aaed2a9f66..51cd0520f5 100644
--- a/packages/flutter/lib/src/widgets/sliver_persistent_header.dart
+++ b/packages/flutter/lib/src/widgets/sliver_persistent_header.dart
@@ -195,7 +195,7 @@ class _SliverPersistentHeaderElement extends RenderObjectElement {
   _RenderSliverPersistentHeaderForWidgetsMixin get renderObject => super.renderObject as _RenderSliverPersistentHeaderForWidgetsMixin;
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     super.mount(parent, newSlot);
     renderObject._element = this;
   }
@@ -247,18 +247,18 @@ class _SliverPersistentHeaderElement extends RenderObjectElement {
   }
 
   @override
-  void insertRenderObjectChild(covariant RenderBox child, dynamic slot) {
+  void insertRenderObjectChild(covariant RenderBox child, Object? slot) {
     assert(renderObject.debugValidateChild(child));
     renderObject.child = child;
   }
 
   @override
-  void moveRenderObjectChild(covariant RenderObject child, dynamic oldSlot, dynamic newSlot) {
+  void moveRenderObjectChild(covariant RenderObject child, Object? oldSlot, Object? newSlot) {
     assert(false);
   }
 
   @override
-  void removeRenderObjectChild(covariant RenderObject child, dynamic slot) {
+  void removeRenderObjectChild(covariant RenderObject child, Object? slot) {
     renderObject.child = null;
   }
 
diff --git a/packages/flutter/lib/src/widgets/sliver_prototype_extent_list.dart b/packages/flutter/lib/src/widgets/sliver_prototype_extent_list.dart
index 7a2ae0da5b..3b313662b8 100644
--- a/packages/flutter/lib/src/widgets/sliver_prototype_extent_list.dart
+++ b/packages/flutter/lib/src/widgets/sliver_prototype_extent_list.dart
@@ -72,7 +72,7 @@ class _SliverPrototypeExtentListElement extends SliverMultiBoxAdaptorElement {
   static final Object _prototypeSlot = Object();
 
   @override
-  void insertRenderObjectChild(covariant RenderObject child, covariant dynamic slot) {
+  void insertRenderObjectChild(covariant RenderObject child, covariant Object slot) {
     if (slot == _prototypeSlot) {
       assert(child is RenderBox);
       renderObject.child = child as RenderBox;
@@ -88,7 +88,7 @@ class _SliverPrototypeExtentListElement extends SliverMultiBoxAdaptorElement {
   }
 
   @override
-  void moveRenderObjectChild(RenderBox child, dynamic oldSlot, dynamic newSlot) {
+  void moveRenderObjectChild(RenderBox child, Object oldSlot, Object newSlot) {
     if (newSlot == _prototypeSlot)
       assert(false); // There's only one prototype child so it cannot be moved.
     else
@@ -96,7 +96,7 @@ class _SliverPrototypeExtentListElement extends SliverMultiBoxAdaptorElement {
   }
 
   @override
-  void removeRenderObjectChild(RenderBox child, dynamic slot) {
+  void removeRenderObjectChild(RenderBox child, Object slot) {
     if (renderObject.child == child)
       renderObject.child = null;
     else
@@ -111,7 +111,7 @@ class _SliverPrototypeExtentListElement extends SliverMultiBoxAdaptorElement {
   }
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     super.mount(parent, newSlot);
     _prototype = updateChild(_prototype, widget.prototypeItem, _prototypeSlot);
   }
diff --git a/packages/flutter/lib/src/widgets/viewport.dart b/packages/flutter/lib/src/widgets/viewport.dart
index 6cc70796d6..1243b2af7c 100644
--- a/packages/flutter/lib/src/widgets/viewport.dart
+++ b/packages/flutter/lib/src/widgets/viewport.dart
@@ -218,7 +218,7 @@ class _ViewportElement extends MultiChildRenderObjectElement {
   RenderViewport get renderObject => super.renderObject as RenderViewport;
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     super.mount(parent, newSlot);
     _updateCenter();
   }
diff --git a/packages/flutter/test/widgets/render_object_element_test.dart b/packages/flutter/test/widgets/render_object_element_test.dart
index 1305d4d91c..a88ae69918 100644
--- a/packages/flutter/test/widgets/render_object_element_test.dart
+++ b/packages/flutter/test/widgets/render_object_element_test.dart
@@ -104,7 +104,7 @@ abstract class SwapperElement extends RenderObjectElement {
   }
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     super.mount(parent, newSlot);
     _updateChildren(widget);
   }
@@ -120,13 +120,13 @@ class SwapperElementWithProperOverrides extends SwapperElement {
   SwapperElementWithProperOverrides(Swapper widget) : super(widget);
 
   @override
-  void insertRenderObjectChild(RenderBox child, dynamic slot) {
+  void insertRenderObjectChild(RenderBox child, Object? slot) {
     insertSlots.add(slot);
     assert(child != null);
     if (slot == 'stable')
       renderObject.stable = child;
     else
-      renderObject.setSwapper(child, slot as bool);
+      renderObject.setSwapper(child, slot! as bool);
   }
 
   @override
@@ -137,12 +137,12 @@ class SwapperElementWithProperOverrides extends SwapperElement {
   }
 
   @override
-  void removeRenderObjectChild(RenderBox child, dynamic slot) {
+  void removeRenderObjectChild(RenderBox child, Object? slot) {
     removeSlots.add(slot);
     if (slot == 'stable')
       renderObject.stable = null;
     else
-      renderObject.setSwapper(null, slot as bool);
+      renderObject.setSwapper(null, slot! as bool);
   }
 }
 
@@ -155,13 +155,13 @@ class SwapperElementWithDeprecatedOverrides extends SwapperElement {
 
   @override
   // ignore: must_call_super
-  void insertChildRenderObject(RenderBox child, dynamic slot) {
+  void insertChildRenderObject(RenderBox child, Object? slot) {
     insertSlots.add(slot);
     assert(child != null);
     if (slot == 'stable')
       renderObject.stable = child;
     else
-      renderObject.setSwapper(child, slot as bool);
+      renderObject.setSwapper(child, slot! as bool);
   }
 
   @override