diff --git a/src/Account.hh b/src/Account.hh
index 3d6d49ec..3e2139fb 100644
--- a/src/Account.hh
+++ b/src/Account.hh
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <memory>
+#include <mutex>
 #include <phosg/JSON.hh>
 #include <shared_mutex>
 #include <string>