diff --git a/ChangeLog b/ChangeLog
index 3d29308970..210287c3ff 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Jul 29 10:44:43 2015  Alex Dowad  <alexinbeijing@gmail.com>
+
+	* gc.c: document argument passed to finalizer proc.
+	  [fix GH-976][ci skip] Patch by @alexdowad
+
 Wed Jul 29 10:36:58 2015  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* io.c (rb_io_extract_modeenc): add option parameter `flags'
diff --git a/gc.c b/gc.c
index 3cb5a61324..ac4f575241 100644
--- a/gc.c
+++ b/gc.c
@@ -2474,7 +2474,9 @@ should_be_finalizable(VALUE obj)
  *     ObjectSpace.define_finalizer(obj, aProc=proc())
  *
  *  Adds <i>aProc</i> as a finalizer, to be called after <i>obj</i>
- *  was destroyed.
+ *  was destroyed. The object ID of the <i>obj</i> will be passed
+ *  as an argument to <i>aProc</i>. If <i>aProc</i> is a lambda or
+ *  method, make sure it can be called with a single argument.
  *
  */