--- a/dom/media/webaudio/AudioParam.h
+++ b/dom/media/webaudio/AudioParam.h
@@ -214,17 +214,17 @@ public:
     return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
   }
 
 private:
   void EventInsertionHelper(ErrorResult& aRv,
                             AudioTimelineEvent::Type aType,
                             double aTime, float aValue,
                             double aTimeConstant = 0.0,
-                            float aDuration = 0.0,
+                            double aDuration = 0.0,
                             const float* aCurve = nullptr,
                             uint32_t aCurveLength = 0)
   {
     AudioTimelineEvent event(aType, aTime, aValue,
                              aTimeConstant, aDuration, aCurve, aCurveLength);
 
     if (!ValidateEvent(event, aRv)) {
       return;