diff --git a/ChangeLog b/ChangeLog
index b6e5dbbad6..5f496a555a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Oct  5 03:24:55 2016  Marc-Andre Lafortune  <ruby-core@marc-andre.ca>
+
+	* enum.c: Make Enumerable#chunk with no block return
+	  an Enumerator [#2172]
+
 Wed Oct  5 01:19:45 2016  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* internal.h (ST2FIX): new macro to convert st_index_t to Fixnum.
diff --git a/NEWS b/NEWS
index ed373f3b34..571eb57a13 100644
--- a/NEWS
+++ b/NEWS
@@ -42,6 +42,8 @@ with all sufficient information, see the ChangeLog file or Redmine
 
   * Enumerable#sum  [Feature #12217]
   * Enumerable#uniq  [Feature #11090]
+  * Enumerable#chunk called without a block now return an Enumerator
+    [Feature #2172]
 
 * Enumerator::Lazy
 
diff --git a/enum.c b/enum.c
index 84f6a6f6af..625097c636 100644
--- a/enum.c
+++ b/enum.c
@@ -2995,14 +2995,14 @@ chunk_i(RB_BLOCK_CALL_FUNC_ARGLIST(yielder, enumerator))
  *      }
  *    }
  *
+ *  If no block is given, an enumerator to `chunk` is returned instead.
  */
 static VALUE
 enum_chunk(VALUE enumerable)
 {
     VALUE enumerator;
 
-    if (!rb_block_given_p())
-	rb_raise(rb_eArgError, "no block given");
+    RETURN_SIZED_ENUMERATOR(enumerable, 0, 0, enum_size);
 
     enumerator = rb_obj_alloc(rb_cEnumerator);
     rb_ivar_set(enumerator, rb_intern("chunk_enumerable"), enumerable);
diff --git a/test/ruby/test_enum.rb b/test/ruby/test_enum.rb
index c87c60ac09..4ff4f88ca9 100644
--- a/test/ruby/test_enum.rb
+++ b/test/ruby/test_enum.rb
@@ -611,6 +611,12 @@ class TestEnumerable < Test::Unit::TestCase
 
     e = @obj.chunk {|elt| :_foo }
     assert_raise(RuntimeError) { e.to_a }
+
+    e = @obj.chunk.with_index {|elt, i| elt - i }
+    assert_equal([[1, [1, 2, 3]],
+                  [-2, [1, 2]]], e.to_a)
+
+    assert_equal(4, (0..3).chunk.size)
   end
 
   def test_slice_before