diff --git a/netwerk/cache2/CacheIOThread.cpp b/netwerk/cache2/CacheIOThread.cpp
index c686c0f8d0..fe0a4ddb05 100644
--- a/netwerk/cache2/CacheIOThread.cpp
+++ b/netwerk/cache2/CacheIOThread.cpp
@@ -215,12 +215,22 @@ nsresult CacheIOThread::Init()
     mBlockingIOWatcher = MakeUnique<detail::BlockingIOWatcher>();
   }
 
+  // Increase the reference count while spawning a new thread.
+  // If PR_CreateThread succeeds, we will forget this reference and the thread
+  // will be responsible to release it when it completes.
+  RefPtr<CacheIOThread> self = this;
+
   mThread = PR_CreateThread(PR_USER_THREAD, ThreadFunc, this,
                             PR_PRIORITY_NORMAL, PR_GLOBAL_THREAD,
                             PR_JOINABLE_THREAD, 128 * 1024);
   if (!mThread) {
     return NS_ERROR_FAILURE;
   }
+  
+  // IMPORTANT: The thread now owns this reference, so it's important that we
+  // leak it here, otherwise we'll end up with a bad refcount.
+  // See the dont_AddRef in ThreadFunc().
+  Unused << self.forget().take();
 
   return NS_OK;
 }
@@ -382,7 +392,9 @@ void CacheIOThread::ThreadFunc(void* aClosure)
 {
   PR_SetCurrentThreadName("Cache2 I/O");
   mozilla::IOInterposer::RegisterCurrentThread();
-  CacheIOThread* thread = static_cast<CacheIOThread*>(aClosure);
+  // We hold on to this reference for the duration of the thread.
+  RefPtr<CacheIOThread> thread =
+      dont_AddRef(static_cast<CacheIOThread*>(aClosure));
   thread->ThreadFunc();
   mozilla::IOInterposer::UnregisterCurrentThread();
 }