diff --git a/src/proto.h b/src/proto.h
index 2b248a5..3313656 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -149,7 +149,7 @@
 # endif
 # include "regexp.pro"
 # include "screen.pro"
-# ifdef FEAT_CRYPT
+# if defined(FEAT_CRYPT) || defined(FEAT_PERSISTENT_UNDO)
 #  include "sha256.pro"
 # endif
 # include "search.pro"