diff --git a/netwerk/cache2/CacheFile.cpp b/netwerk/cache2/CacheFile.cpp
index 2831bc8772a..689b5d7398c 100644
--- a/netwerk/cache2/CacheFile.cpp
+++ b/netwerk/cache2/CacheFile.cpp
@@ -1783,6 +1783,8 @@ CacheFile::DataSize(int64_t* aSize)
 bool
 CacheFile::IsDoomed()
 {
+  CacheFileAutoLock lock(this);
+
   if (!mHandle)
     return false;