diff --git a/pkg/dev_compiler/lib/runtime/dart_runtime.js b/pkg/dev_compiler/lib/runtime/dart_runtime.js
index 4dd786854bbc..cd8ac458821d 100644
--- a/pkg/dev_compiler/lib/runtime/dart_runtime.js
+++ b/pkg/dev_compiler/lib/runtime/dart_runtime.js
@@ -967,7 +967,8 @@ var dart, _js_helper, _js_primitives;
   dart.JsSymbol = Symbol;
 
   function import_(value) {
-    if (!value) throw 'missing required module';
+    // TODO(jmesserly): throw once we're loading all of core libs.
+    if (!value && console) console.warn('missing required module');
     return value;
   }
   dart.import = import_;
diff --git a/pkg/dev_compiler/test/browser/runtime_tests.js b/pkg/dev_compiler/test/browser/runtime_tests.js
index 824edd574a3d..9b84c9bc6b58 100644
--- a/pkg/dev_compiler/test/browser/runtime_tests.js
+++ b/pkg/dev_compiler/test/browser/runtime_tests.js
@@ -391,3 +391,13 @@ suite('instanceOf', () => {
     assert.equal(intType, core.int);
   });
 });
+
+suite('primitives', function() {
+  'use strict';
+
+  test('fixed length list', () => {
+    let list = new core.List(10);
+    list[0] = 42;
+    assert.throws(() => list.add(42));
+  });
+});
diff --git a/pkg/dev_compiler/test/generated_sdk/lib/_internal/compiler/js_lib/js_array.dart b/pkg/dev_compiler/test/generated_sdk/lib/_internal/compiler/js_lib/js_array.dart
index c9aab5f74eea..fae79523869f 100644
--- a/pkg/dev_compiler/test/generated_sdk/lib/_internal/compiler/js_lib/js_array.dart
+++ b/pkg/dev_compiler/test/generated_sdk/lib/_internal/compiler/js_lib/js_array.dart
@@ -85,7 +85,7 @@ class JSArray<E> implements List<E>, JSIndexable {
   }
 
   checkGrowable(reason) {
-    if (this is !JSExtendableArray) {
+    if (JS('bool', r'#.fixed$length', this)) {
       throw new UnsupportedError(reason);
     }
   }
diff --git a/pkg/dev_compiler/tool/input_sdk/private/js_array.dart b/pkg/dev_compiler/tool/input_sdk/private/js_array.dart
index c9aab5f74eea..fae79523869f 100644
--- a/pkg/dev_compiler/tool/input_sdk/private/js_array.dart
+++ b/pkg/dev_compiler/tool/input_sdk/private/js_array.dart
@@ -85,7 +85,7 @@ class JSArray<E> implements List<E>, JSIndexable {
   }
 
   checkGrowable(reason) {
-    if (this is !JSExtendableArray) {
+    if (JS('bool', r'#.fixed$length', this)) {
       throw new UnsupportedError(reason);
     }
   }