diff --git a/compiler/api/compiler.py b/compiler/api/compiler.py
index ad5964bf..f5f45ae4 100644
--- a/compiler/api/compiler.py
+++ b/compiler/api/compiler.py
@@ -264,7 +264,7 @@ def start():
             docstring_args.append(
                 "{}: {}{}".format(
                     arg_name,
-                    "``optional``".format(flag_number) if is_optional else "",
+                    "``optional`` ".format(flag_number) if is_optional else "",
                     get_docstring_arg_type(arg_type)
                 )
             )