diff --git a/xwords4/common/server.h b/xwords4/common/server.h
index 1184c2b7a..8ac90bca2 100644
--- a/xwords4/common/server.h
+++ b/xwords4/common/server.h
@@ -25,6 +25,7 @@
 
 #include "commmgr.h"
 #include "model.h"
+#include "engine.h"
 
 #ifdef CPLUS
 extern "C" {