diff --git a/ChangeLog b/ChangeLog
index aa2e76a7f4..b204dd8f8d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Sat Apr 19 15:38:29 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* parse.y (primary): flush cmdarg flags inside left-paren in a
+	  command argument, to allow parenthesed do-block as an argument
+	  without arguments parentheses.  [ruby-core:61950] [Bug #9726]
+
 Sat Apr 19 10:07:24 2014  Tanaka Akira  <akr@fsij.org>
 
 	* internal.h (struct RBignum): Use size_t for len.
diff --git a/parse.y b/parse.y
index 5b90bd2909..726f89130b 100644
--- a/parse.y
+++ b/parse.y
@@ -2620,12 +2620,18 @@ primary		: literal
 			$$ = dispatch1(paren, 0);
 		    %*/
 		    }
-		| tLPAREN_ARG expr {lex_state = EXPR_ENDARG;} rparen
+		| tLPAREN_ARG
 		    {
+			$<val>1 = cmdarg_stack;
+			cmdarg_stack = 0;
+		    }
+		  expr {lex_state = EXPR_ENDARG;} rparen
+		    {
+			cmdarg_stack = $<val>1;
 		    /*%%%*/
-			$$ = $2;
+			$$ = $3;
 		    /*%
-			$$ = dispatch1(paren, $2);
+			$$ = dispatch1(paren, $3);
 		    %*/
 		    }
 		| tLPAREN compstmt ')'
diff --git a/test/ruby/test_syntax.rb b/test/ruby/test_syntax.rb
index bc1d80f990..0847c28bfc 100644
--- a/test/ruby/test_syntax.rb
+++ b/test/ruby/test_syntax.rb
@@ -78,6 +78,11 @@ class TestSyntax < Test::Unit::TestCase
     end
   end
 
+  def test_do_block_in_cmdarg
+    bug9726 = '[ruby-core:61950] [Bug #9726]'
+    assert_valid_syntax("tap (proc do end)", __FILE__, bug9726)
+  end
+
   def test_keyword_rest
     bug5989 = '[ruby-core:42455]'
     assert_valid_syntax("def kwrest_test(**a) a; end", __FILE__, bug5989)