--- a/layout/style/StyleAnimationValue.cpp
+++ b/layout/style/StyleAnimationValue.cpp
@@ -5197,20 +5197,21 @@ StyleAnimationValue::operator==(const St
 // AnimationValue Implementation
 
 bool
 AnimationValue::operator==(const AnimationValue& aOther) const
 {
   // It is possible to compare an empty AnimationValue with others, so both
   // mServo and mGecko could be null while comparing.
   MOZ_ASSERT(!mServo || mGecko.IsNull());
-  if (mServo) {
+  if (mServo && aOther.mServo) {
     return Servo_AnimationValue_DeepEqual(mServo, aOther.mServo);
   }
-  return mGecko == aOther.mGecko;
+  return !mServo && !aOther.mServo &&
+         mGecko == aOther.mGecko;
 }
 
 float
 AnimationValue::GetOpacity() const
 {
   MOZ_ASSERT(!mServo != mGecko.IsNull());
   return mServo ? Servo_AnimationValue_GetOpacity(mServo)
                 : mGecko.GetFloatValue();