diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
index 1dde919..3dc8618 100644
--- a/Doc/library/stdtypes.rst
+++ b/Doc/library/stdtypes.rst
@@ -471,7 +471,7 @@
     Equivalent to::
 
         def bit_length(self):
-            s = bin(x)          # binary representation:  bin(-37) --> '-0b100101'
+            s = bin(self)       # binary representation:  bin(-37) --> '-0b100101'
             s = s.lstrip('-0b') # remove leading zeros and minus sign
             return len(s)       # len('100101') --> 6