diff --git a/web-animations-1/Overview.bs b/web-animations-1/Overview.bs
index 211988676f7..4f2dbd8687c 100644
--- a/web-animations-1/Overview.bs
+++ b/web-animations-1/Overview.bs
@@ -3960,7 +3960,7 @@ dictionary DocumentTimelineOptions {
 };
 
 [Exposed=Window,
- Constructor(optional DocumentTimelineOptions options)]
+ Constructor(optional DocumentTimelineOptions options = {})]
 interface DocumentTimeline : AnimationTimeline {
 };
 </pre>
@@ -4322,7 +4322,7 @@ abstract {{AnimationEffect}} interface.
 interface AnimationEffect {
     EffectTiming         getTiming();
     ComputedEffectTiming getComputedTiming();
-    void                 updateTiming(optional OptionalEffectTiming timing);
+    void                 updateTiming(optional OptionalEffectTiming timing = {});
 };
 </pre>
 
@@ -4697,7 +4697,7 @@ dictionary ComputedEffectTiming : EffectTiming {
 [Exposed=Window,
  Constructor((Element or CSSPseudoElement)? target,
              object? keyframes,
-             optional (unrestricted double or KeyframeEffectOptions) options),
+             optional (unrestricted double or KeyframeEffectOptions) options = {}),
  Constructor(KeyframeEffect source)]
 interface KeyframeEffect : AnimationEffect {
     attribute (Element or CSSPseudoElement)? target;
@@ -5717,8 +5717,8 @@ the {{Animatable}} interface mixin.
 <pre class='idl'>
 interface mixin Animatable {
     Animation           animate(object? keyframes,
-                                optional (unrestricted double or KeyframeAnimationOptions) options);
-    sequence&lt;Animation&gt; getAnimations(optional GetAnimationsOptions options);
+                                optional (unrestricted double or KeyframeAnimationOptions) options = {});
+    sequence&lt;Animation&gt; getAnimations(optional GetAnimationsOptions options = {});
 };
 
 dictionary KeyframeAnimationOptions : KeyframeEffectOptions {
@@ -5932,7 +5932,7 @@ CSSPseudoElement includes Animatable;
 
 <pre class='idl'>
 [Exposed=Window,
- Constructor(DOMString type, optional AnimationPlaybackEventInit eventInitDict)]
+ Constructor(DOMString type, optional AnimationPlaybackEventInit eventInitDict = {})]
 interface AnimationPlaybackEvent : Event {
     readonly attribute double? currentTime;
     readonly attribute double? timelineTime;