diff --git a/Source/WebCore/Modules/mediasource/SourceBuffer.cpp b/Source/WebCore/Modules/mediasource/SourceBuffer.cpp
index 685940723e7c7..e9e4437132973 100644
--- a/Source/WebCore/Modules/mediasource/SourceBuffer.cpp
+++ b/Source/WebCore/Modules/mediasource/SourceBuffer.cpp
@@ -447,6 +447,7 @@ void SourceBuffer::removedFromMediaSource()
     m_private->removedFromMediaSource();
     m_private->setIsAttached(false);
     m_source = nullptr;
+    m_extraMemoryCost = 0;
 }
 
 void SourceBuffer::seekToTime(const MediaTime& time)