diff --git a/ChangeLog b/ChangeLog
index 129208e492..3511201d8f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Jan 10 06:23:21 2014  Benoit Daloze  <eregontp@gmail.com>
+
+	* range.c (Range#size): [DOC] improve description and add examples.
+	  Patch by @skade. [Fixes GH-501]
+
 Fri Jan 10 00:47:52 2014  Josef Stribny  <strzibny@gmail.com>
 
 	* ext/tk/extconf.rb: fix to pass arrays instead of strings to
diff --git a/range.c b/range.c
index 4526dcba89..d2d9a707c0 100644
--- a/range.c
+++ b/range.c
@@ -711,9 +711,12 @@ sym_each_i(RB_BLOCK_CALL_FUNC_ARGLIST(v, arg))
  *  call-seq:
  *     rng.size                   -> num
  *
- *  Returns the number of elements in the range.
+ *  Returns the number of elements in the range. Both the begin and the end of
+ *  the Range must be Numeric, otherwise nil is returned.
  *
  *    (10..20).size    #=> 11
+ *    ('a'..'z').size  #=> nil
+ *    (-Float::INFINITY..Float::INFINITY).size #=> Infinity
  */
 
 static VALUE