diff --git a/packages/animations/browser/src/dsl/animation_timeline_builder.ts b/packages/animations/browser/src/dsl/animation_timeline_builder.ts
index e4e9b90bdde..b20800e1ebc 100644
--- a/packages/animations/browser/src/dsl/animation_timeline_builder.ts
+++ b/packages/animations/browser/src/dsl/animation_timeline_builder.ts
@@ -615,8 +615,7 @@ export class AnimationTimelineContext {
 
 export class TimelineBuilder {
   public duration: number = 0;
-  // TODO(issue/24571): remove '!'.
-  public easing!: string|null;
+  public easing: string|null = null;
   private _previousKeyframe: ɵStyleDataMap = new Map();
   private _currentKeyframe: ɵStyleDataMap = new Map();
   private _keyframes = new Map<number, ɵStyleDataMap>();
diff --git a/packages/animations/browser/src/render/transition_animation_engine.ts b/packages/animations/browser/src/render/transition_animation_engine.ts
index 9bbd8f5ee71..eee66263a16 100644
--- a/packages/animations/browser/src/render/transition_animation_engine.ts
+++ b/packages/animations/browser/src/render/transition_animation_engine.ts
@@ -1499,8 +1499,7 @@ export class TransitionAnimationPlayer implements AnimationPlayer {
 
   private _queuedCallbacks = new Map<string, ((event: any) => any)[]>();
   public readonly destroyed = false;
-  // TODO(issue/24571): remove '!'.
-  public parentPlayer!: AnimationPlayer;
+  public parentPlayer: AnimationPlayer|null = null;
 
   public markedForDestroy: boolean = false;
   public disabled = false;
diff --git a/packages/animations/browser/src/render/web_animations/web_animations_player.ts b/packages/animations/browser/src/render/web_animations/web_animations_player.ts
index 59d201eb08e..bf772744a81 100644
--- a/packages/animations/browser/src/render/web_animations/web_animations_player.ts
+++ b/packages/animations/browser/src/render/web_animations/web_animations_player.ts
@@ -30,7 +30,7 @@ export class WebAnimationsPlayer implements AnimationPlayer {
   private _originalOnDoneFns: Function[] = [];
   private _originalOnStartFns: Function[] = [];
 
-  // TODO(issue/24571): remove '!'.
+  // using non-null assertion because it's re(set) by init();
   public readonly domPlayer!: DOMAnimation;
   public time = 0;
 
@@ -64,8 +64,8 @@ export class WebAnimationsPlayer implements AnimationPlayer {
     this._initialized = true;
 
     const keyframes = this.keyframes;
-    (this as {domPlayer: DOMAnimation}).domPlayer =
-        this._triggerWebAnimation(this.element, keyframes, this.options);
+    // @ts-expect-error overwriting a readonly property
+    this.domPlayer = this._triggerWebAnimation(this.element, keyframes, this.options);
     this._finalKeyframe = keyframes.length ? keyframes[keyframes.length - 1] : new Map();
     this.domPlayer.addEventListener('finish', () => this._onFinish());
   }