diff --git a/src/cyclic_hash.h b/src/cyclic_hash.h
index 5bf22116..ba88a47d 100644
--- a/src/cyclic_hash.h
+++ b/src/cyclic_hash.h
@@ -2,6 +2,8 @@
 #ifndef CYCLICHASH
 #define CYCLICHASH
 
+#error EXPERIMENTAL. DO NOT USE
+
 #include "characterhash.h"
 
 /**