diff --git a/py/_code/source.py b/py/_code/source.py
index 7fc7b23a..7f4d619f 100644
--- a/py/_code/source.py
+++ b/py/_code/source.py
@@ -16,7 +16,7 @@
 
 
 class Source(object):
-    """ a immutable object holding a source code fragment,
+    """ an immutable object holding a source code fragment,
         possibly deindenting it.
     """
     _compilecounter = 0