diff --git a/src/ast/ast.h b/src/ast/ast.h
index 810db59504..1ca192a462 100644
--- a/src/ast/ast.h
+++ b/src/ast/ast.h
@@ -1807,7 +1807,7 @@ class NaryOperation final : public Expression {
 
   NaryOperation(Zone* zone, Token::Value op, Expression* first,
                 size_t initial_subsequent_size)
-      : Expression(kNoSourcePosition, kNaryOperation),
+      : Expression(first->position(), kNaryOperation),
         first_(first),
         subsequent_(zone) {
     bit_field_ |= OperatorField::encode(op);
diff --git a/test/mjsunit/regress/regress-crbug-791256.js b/test/mjsunit/regress/regress-crbug-791256.js
new file mode 100644
index 0000000000..bf9fc25977
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-791256.js
@@ -0,0 +1,12 @@
+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Original repro. A DCHECK used to fire.
+(function* (name = (eval(foo), foo, prototype)) { });
+
+// Simpler repro.
+(function (name = (foo, bar, baz) ) { });
+
+// A test which uses the value of the n-ary operation.
+(function (param = (0, 1, 2)) { assertEquals(2, param); })();