diff --git a/p2p_manager_unittest.cc b/p2p_manager_unittest.cc
index 262031f..af83d4a 100644
--- a/p2p_manager_unittest.cc
+++ b/p2p_manager_unittest.cc
@@ -437,7 +437,8 @@
 
   // Emulate p2p-client returning valid URL with "fooX", 42 and "cros_au"
   // being propagated in the right places.
-  test_conf_->SetP2PClientCommandLine("echo 'http://1.2.3.4/%s_%zu'");
+  test_conf_->SetP2PClientCommandLine(
+      "echo 'http://1.2.3.4/{file_id}_{minsize}'");
   manager->LookupUrlForFile("fooX", 42, TimeDelta(),
                             base::Bind(ExpectUrl,
                                        "http://1.2.3.4/fooX.cros_au_42", loop));