--- a/dom/animation/KeyframeEffect.cpp
+++ b/dom/animation/KeyframeEffect.cpp
@@ -369,18 +369,17 @@ void KeyframeEffect::EnsureBaseStyles(
   if (aBaseStylesChanged != nullptr) {
     *aBaseStylesChanged = false;
   }
 
   if (!mTarget) {
     return;
   }
 
-  Maybe<nsRefPtrHashtable<nsUint32HashKey, RawServoAnimationValue>>
-      previousBaseStyles;
+  Maybe<BaseValuesHashmap> previousBaseStyles;
   if (aBaseStylesChanged != nullptr) {
     previousBaseStyles.emplace(std::move(mBaseValues));
   }
 
   mBaseValues.Clear();
 
   nsPresContext* presContext =
       nsContentUtils::GetContextForContent(mTarget->mElement);

--- a/dom/animation/KeyframeEffect.h
+++ b/dom/animation/KeyframeEffect.h
@@ -397,17 +397,19 @@ class KeyframeEffect : public AnimationE
 
   // We need to track when we go to or from being "in effect" since
   // we need to re-evaluate the cascade of animations when that changes.
   bool mInEffectOnLastAnimationTimingUpdate;
 
   // The non-animated values for properties in this effect that contain at
   // least one animation value that is composited with the underlying value
   // (i.e. it uses the additive or accumulate composite mode).
-  nsRefPtrHashtable<nsUint32HashKey, RawServoAnimationValue> mBaseValues;
+  using BaseValuesHashmap =
+      nsRefPtrHashtable<nsUint32HashKey, RawServoAnimationValue>;
+  BaseValuesHashmap mBaseValues;
 
   // True if this effect is in the EffectSet for its target element. This is
   // used as an optimization to avoid unnecessary hashmap lookups on the
   // EffectSet.
   bool mInEffectSet = false;
 
  private:
   nsChangeHint mCumulativeChangeHint;