diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
index e5a280e1949de9..614e0d4db102cb 100644
--- a/Lib/collections/__init__.py
+++ b/Lib/collections/__init__.py
@@ -550,6 +550,9 @@ class Counter(dict):
     or multiset.  Elements are stored as dictionary keys and their counts
     are stored as dictionary values.
 
+    When constructed from a Mapping or Counter, the original object's
+    values will be used as the initial counts.
+
     >>> c = Counter('abcdeabcdabcaba')  # count elements from a string
 
     >>> c.most_common(3)                # three most common elements