--- a/image/DecodePool.cpp
+++ b/image/DecodePool.cpp
@@ -342,16 +342,19 @@ DecodePool::DecodePool()
       // even if under load we can't actually get that level of parallelism.
       limit = 2;
     } else {
       limit = numCores - 1;
     }
   } else {
     limit = static_cast<uint32_t>(prefLimit);
   }
+  if (limit > 32) {
+    limit = 32;
+  }
 
   // Initialize the thread pool.
   for (uint32_t i = 0 ; i < limit ; ++i) {
     nsCOMPtr<nsIRunnable> worker = new DecodePoolWorker(mImpl);
     nsCOMPtr<nsIThread> thread;
     nsresult rv = NS_NewThread(getter_AddRefs(thread), worker);
     MOZ_RELEASE_ASSERT(NS_SUCCEEDED(rv) && thread,
                        "Should successfully create image decoding threads");