diff --git a/ChangeLog b/ChangeLog
index 266599c716..1dfc038a51 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Tue Mar 29 13:50:30 2016  Eric Wong  <e@80x24.org>
+
+	* io.c (io_getpartial): remove unused kwarg from template
+	* test/ruby/test_io.rb (test_readpartial_bad_args): new
+	  [Bug #11885]
+
 Tue Mar 29 13:41:03 2016  Tadashi Saito  <tadashi_saito@dwango.co.jp>
 
 	* compile.c, cont.c, doc, man: fix common misspelling.
diff --git a/io.c b/io.c
index 2bf7cd7512..5c8a66d143 100644
--- a/io.c
+++ b/io.c
@@ -2506,7 +2506,7 @@ io_getpartial(int argc, VALUE *argv, VALUE io, VALUE opts, int nonblock)
     long n, len;
     struct read_internal_arg arg;
 
-    rb_scan_args(argc, argv, "11:", &length, &str, NULL);
+    rb_scan_args(argc, argv, "11", &length, &str);
 
     if ((len = NUM2LONG(length)) < 0) {
 	rb_raise(rb_eArgError, "negative length %ld given", len);
diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index 766804eb2e..2b79acea09 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -3186,6 +3186,17 @@ End
     }
   end
 
+  def test_readpartial_bad_args
+    IO.pipe do |r, w|
+      w.write '.'
+      buf = String.new
+      assert_raise(ArgumentError) { r.readpartial(1, buf, exception: false) }
+      assert_raise(TypeError) { r.readpartial(1, exception: false) }
+      assert_equal [[r],[],[]], IO.select([r], nil, nil, 1)
+      assert_equal '.', r.readpartial(1)
+    end
+  end
+
   def test_sysread_unlocktmp_ensure
     bug8669 = '[ruby-core:56121] [Bug #8669]'
 
diff --git a/version.h b/version.h
index a83715b28c..50f4efd3d7 100644
--- a/version.h
+++ b/version.h
@@ -1,6 +1,6 @@
 #define RUBY_VERSION "2.3.0"
 #define RUBY_RELEASE_DATE "2016-03-29"
-#define RUBY_PATCHLEVEL 10
+#define RUBY_PATCHLEVEL 11
 
 #define RUBY_RELEASE_YEAR 2016
 #define RUBY_RELEASE_MONTH 3