diff --git a/src/thread/WindowsFuture.hxx b/src/thread/WindowsFuture.hxx
index dd2543cf4..78d367228 100644
--- a/src/thread/WindowsFuture.hxx
+++ b/src/thread/WindowsFuture.hxx
@@ -24,6 +24,7 @@
 #include "WindowsCond.hxx"
 
 #include <memory>
+#include <system_error> // for std::error_category
 #include <variant>
 
 enum class WinFutureErrc : int {