Minor formatting fix=up
diff --git a/Lib/collections.py b/Lib/collections.py
index 3471c89..ba6d7ca 100644
--- a/Lib/collections.py
+++ b/Lib/collections.py
@@ -337,7 +337,7 @@
     seen = set()
     for name in field_names:
         if name.startswith('_') and not rename:
-            raise ValueError('Field names cannot start with an underscore:'
+            raise ValueError('Field names cannot start with an underscore: '
                              '%r' % name)
         if name in seen:
             raise ValueError('Encountered duplicate field name: %r' % name)