diff --git a/spdy/core/fifo_write_scheduler.h b/spdy/core/fifo_write_scheduler.h
index e972a2b..3c38bd5 100644
--- a/spdy/core/fifo_write_scheduler.h
+++ b/spdy/core/fifo_write_scheduler.h
@@ -208,7 +208,7 @@
 }
 
 template <typename StreamIdType>
-string FifoWriteScheduler<StreamIdType>::DebugString() const {
+SpdyString FifoWriteScheduler<StreamIdType>::DebugString() const {
   return SpdyStrCat(
       "FifoWriteScheduler {num_streams=", registered_streams_.size(),
       " num_ready_streams=", NumReadyStreams(), "}");