diff --git a/bignum.c b/bignum.c
index daaff252b6..3f1bb38341 100644
--- a/bignum.c
+++ b/bignum.c
@@ -6999,6 +6999,13 @@ rb_big_size(VALUE big)
  *     (2**10000).bit_length     #=> 10001
  *     (2**10000+1).bit_length   #=> 10001
  *
+ *  This method can be used to detect overflow in Array#pack as follows.
+ *
+ *     if n.bit_length < 32
+ *       [n].pack("l") # no overflow
+ *     else
+ *       raise "overflow"
+ *     end
  */
 
 static VALUE
diff --git a/numeric.c b/numeric.c
index cc9c63e3d1..4bb2c3a534 100644
--- a/numeric.c
+++ b/numeric.c
@@ -3538,6 +3538,14 @@ fix_size(VALUE fix)
  *     (2**12-1).bit_length      #=> 12
  *     (2**12).bit_length        #=> 13
  *     (2**12+1).bit_length      #=> 13
+ *
+ *  This method can be used to detect overflow in Array#pack as follows.
+ *
+ *     if n.bit_length < 32
+ *       [n].pack("l") # no overflow
+ *     else
+ *       raise "overflow"
+ *     end
  */
 
 static VALUE