1 files changed, 4 insertions, 1 deletions
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