diff --git a/base/message_loop.cc b/base/message_loop.cc
index dd8ba3a..a207659 100644
--- a/base/message_loop.cc
+++ b/base/message_loop.cc
@@ -151,10 +151,12 @@
 #define MESSAGE_PUMP_UI base::MessagePumpMac::Create()
 #define MESSAGE_PUMP_IO new base::MessagePumpLibevent()
 #elif defined(OS_NACL)
-// Currently NaCl doesn't have a UI or an IO MessageLoop.
-// TODO(abarth): Figure out if we need these.
+// Currently NaCl doesn't have a UI MessageLoop.
+// TODO(abarth): Figure out if we need this.
 #define MESSAGE_PUMP_UI NULL
-#define MESSAGE_PUMP_IO NULL
+// ipc_channel_nacl.cc uses a worker thread to do socket reads currently, and
+// doesn't require extra support for watching file descriptors.
+#define MESSAGE_PUMP_IO new base::MessagePumpDefault();
 #elif defined(OS_POSIX)  // POSIX but not MACOSX.
 #define MESSAGE_PUMP_UI new base::MessagePumpForUI()
 #define MESSAGE_PUMP_IO new base::MessagePumpLibevent()