diff --git a/shtab/__init__.py b/shtab/__init__.py
index 04fb421..1fc16ac 100644
--- a/shtab/__init__.py
+++ b/shtab/__init__.py
@@ -384,8 +384,8 @@ def complete_bash(parser, root_prefix=None, preamble="", choice_functions=None):
   local completing_word="${COMP_WORDS[COMP_CWORD]}"
   COMPREPLY=()
 
-  prefix=${root_prefix}
-  word_index=0
+  local prefix=${root_prefix}
+  local word_index=0
   _set_parser_defaults
   word_index=1