diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 853c0c0aaf..e34688051d 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -5657,7 +5657,7 @@ HValue* HOptimizedGraphBuilder::HandlePolymorphicElementAccess(
             elements, isolate()->factory()->fixed_array_map(),
             zone(), top_info(), mapcompare));
       }
-      if (map->IsJSArray()) {
+      if (map->instance_type() == JS_ARRAY_TYPE) {
         HInstruction* length = AddLoad(
             object, HObjectAccess::ForArrayLength(elements_kind), mapcompare);
         checked_key = Add<HBoundsCheck>(key, length);
diff --git a/test/mjsunit/regress/regress-crbug-263276.js b/test/mjsunit/regress/regress-crbug-263276.js
new file mode 100644
index 0000000000..05aa94cc85
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-263276.js
@@ -0,0 +1,46 @@
+// Copyright 2013 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Flags: --allow-natives-syntax
+
+var array1 = [];
+array1.foo = true;
+
+var array2 = [];
+array2.bar = true;
+
+function bad(array) {
+  array[array.length] = 1;
+}
+
+bad(array1);
+bad(array1);
+bad(array2);  // Length is now 1.
+bad(array2);  // Length is now 2.
+%OptimizeFunctionOnNextCall(bad);
+bad(array2);  // Length is now 3.
+assertEquals(3, array2.length);