diff --git a/Lib/ConfigParser.py b/Lib/ConfigParser.py
index e080fcb..9a365c0 100644
--- a/Lib/ConfigParser.py
+++ b/Lib/ConfigParser.py
@@ -569,7 +569,7 @@
                     value = value % vars
                 except KeyError as e:
                     raise InterpolationMissingOptionError(
-                        option, section, rawval, e[0])
+                        option, section, rawval, e.message)
             else:
                 break
         if "%(" in value: