diff --git a/ruby.c b/ruby.c
index fb9c77fdd7..ad331433dc 100644
--- a/ruby.c
+++ b/ruby.c
@@ -376,7 +376,6 @@ usage(const char *name, int help, int highlight, int columns)
         M("yydebug(+error-tolerant)",                "", "yydebug of yacc parser generator."),
         M("parsetree(+error-tolerant)",              "", "Abstract syntax tree (AST)."),
         M("parsetree_with_comment(+error-tolerant)", "", "AST with comments."),
-        M("prism_parsetree",                         "", "Prism AST."),
     };
     static const struct ruby_opt_message features[] = {
         M("gems",                  "", "Rubygems (only for debugging, default: "DEFAULT_RUBYGEMS_ENABLED")."),