More source links.
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index 4096cbb..4a92b05 100644
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -12,7 +12,7 @@
    import itertools
    __name__ = '<doctest>'
 
-**Source code:** :source:`Lib/collections.py`
+**Source code:** :source:`Lib/collections.py` and :source:`Lib/_abcoll.py`
 
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