diff --git a/engine/qux/qux.h b/engine/qux/qux.h
index aec98bdc3..571d40477 100644
--- a/engine/qux/qux.h
+++ b/engine/qux/qux.h
@@ -15,7 +15,7 @@
 #endif
 
 #include "Xproto.h"
-#include "X.h"
+#include "x.h"
 
 #include "bigreqstr.h"