diff --git a/src/tools/cli_formatter.hpp b/src/tools/cli_formatter.hpp
index 93ebe0c..946b596 100644
--- a/src/tools/cli_formatter.hpp
+++ b/src/tools/cli_formatter.hpp
@@ -60,7 +60,7 @@ class GappaFormatter : public CLI::Formatter
     {
         auto res = CLI::Formatter::make_option_opts( opt );
         if(opt->get_type_size() == 0) {
-            res = "FLAG " + res;
+            res = " FLAG " + res;
         }
         return res;
     }