diff --git a/Lib/argparse.py b/Lib/argparse.py
index 4f3aea9..e45b67b 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -2130,7 +2130,7 @@
                 action = self._option_string_actions[option_string]
                 return action, option_string, explicit_arg
 
-        if self.allow_abbrev:
+        if self.allow_abbrev or not arg_string.startswith('--'):
             # search through all possible prefixes of the option string
             # and all actions in the parser for possible interpretations
             option_tuples = self._get_option_tuples(arg_string)