diff --git a/package.json b/package.json
index 8af1bcc..0b11ec1 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "jsdom-testing-mocks",
-  "version": "1.15.0",
+  "version": "1.15.1",
   "author": "Ivan Galiatin",
   "license": "MIT",
   "description": "A set of tools for emulating browser behavior in jsdom environment",
diff --git a/src/mocks/web-animations-api/AnimationEffect.ts b/src/mocks/web-animations-api/AnimationEffect.ts
index bc2c511..32345fb 100644
--- a/src/mocks/web-animations-api/AnimationEffect.ts
+++ b/src/mocks/web-animations-api/AnimationEffect.ts
@@ -18,7 +18,9 @@ class MockedAnimationEffect implements AnimationEffect {
     }
   }
 
-  #getNormalizedDuration(): number {
+  // Changed from private (#getNormalizedDuration) to protected (_getNormalizedDuration)
+  // to allow access from child classes in all JavaScript environments
+  protected _getNormalizedDuration(): number {
     // the only possible value is "auto"
     if (typeof this.#timing.duration === 'string') {
       return 0;
@@ -34,7 +36,7 @@ class MockedAnimationEffect implements AnimationEffect {
 
   getComputedTiming(): ComputedEffectTiming {
     // duration of the animation
-    const duration = this.#getNormalizedDuration();
+    const duration = this._getNormalizedDuration();
 
     // Calculated as (iteration_duration * iteration_count)
     const activeDuration =