diff --git a/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart b/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
index fd49c22f886..0ea1989c086 100644
--- a/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
@@ -304,8 +304,8 @@ class OldEmitter implements Emitter {
 
   /** Needs defineClass to be defined. */
   jsAst.Expression buildInheritFrom() {
-    return js(r'''
-        var inheritFrom = function() {
+    jsAst.Expression result = js(r'''
+        function() {
           function tmp() {}
           var hasOwnProperty = Object.prototype.hasOwnProperty;
           return function (constructor, superConstructor) {
@@ -323,6 +323,10 @@ class OldEmitter implements Emitter {
           };
         }()
       ''');
+    if (compiler.hasIncrementalSupport) {
+      result = js(r'self.$dart_unsafe_eval.inheritFrom = #', [result]);
+    }
+    return js(r'var inheritFrom = #', [result]);
   }
 
   /// Code that needs to be run before first invocation of
diff --git a/pkg/compiler/lib/src/universe/universe.dart b/pkg/compiler/lib/src/universe/universe.dart
index e5e3915d851..5b60d70850b 100644
--- a/pkg/compiler/lib/src/universe/universe.dart
+++ b/pkg/compiler/lib/src/universe/universe.dart
@@ -747,6 +747,13 @@ class TypedSelector extends Selector {
       new Map<Selector, Map<TypeMask, TypedSelector>>();
 
   factory TypedSelector(TypeMask mask, Selector selector, World world) {
+    if (!world.hasClosedWorldAssumption) {
+      bool isNullable = mask.isNullable;
+      mask = world.compiler.typesTask.dynamicType;
+      if (isNullable) {
+        mask = mask.nullable();
+      }
+    }
     // TODO(johnniwinther): Allow more TypeSelector kinds during resoluton.
     assert(world.isClosed || mask.isExact);
     if (selector.mask == mask) return selector;
diff --git a/pkg/compiler/lib/src/warnings.dart b/pkg/compiler/lib/src/warnings.dart
index 5d872d01063..f98667248e7 100644
--- a/pkg/compiler/lib/src/warnings.dart
+++ b/pkg/compiler/lib/src/warnings.dart
@@ -4,7 +4,7 @@
 
 part of dart2js;
 
-const DONT_KNOW_HOW_TO_FIX = "";
+const DONT_KNOW_HOW_TO_FIX = "Computer says no!";
 
 /**
  * The messages in this file should meet the following guide lines:
diff --git a/pkg/compiler/lib/src/world.dart b/pkg/compiler/lib/src/world.dart
index 4391cdb3fc3..70bdcaa6ac3 100644
--- a/pkg/compiler/lib/src/world.dart
+++ b/pkg/compiler/lib/src/world.dart
@@ -96,6 +96,10 @@ abstract class ClassWorld {
 
   /// Returns `true` if any subclass of [superclass] implements [type].
   bool hasAnySubclassThatImplements(ClassElement superclass, ClassElement type);
+
+  /// Returns `true` if closed-world assumptions can be made, that is,
+  /// incremental compilation isn't enabled.
+  bool get hasClosedWorldAssumption;
 }
 
 class World implements ClassWorld {
@@ -521,4 +525,6 @@ class World implements ClassWorld {
     }
     return functionsThatMightBePassedToApply.contains(element);
   }
+
+  bool get hasClosedWorldAssumption => !compiler.hasIncrementalSupport;
 }
diff --git a/pkg/dart2js_incremental/lib/library_updater.dart b/pkg/dart2js_incremental/lib/library_updater.dart
index c206760c08d..df7a85a6dd0 100644
--- a/pkg/dart2js_incremental/lib/library_updater.dart
+++ b/pkg/dart2js_incremental/lib/library_updater.dart
@@ -417,7 +417,14 @@ class LibraryUpdater extends JsFeatures {
     }
 
     for (ClassElementX cls in newClasses) {
-      // TODO(ahe): Set up superclasses.
+      if (cls.isObject) continue;
+      jsAst.Node classAccess = namer.elementAccess(cls);
+      jsAst.Node superAccess = namer.elementAccess(cls.superclass);
+
+      updates.add(
+          js.statement(
+              r'self.$dart_unsafe_eval.inheritFrom(#, #)',
+              [classAccess, superAccess]));
     }
 
     for (Element element in compiler.enqueuer.codegen.newlyEnqueuedElements) {
diff --git a/tests/try/web/incremental_compilation_update_test.dart b/tests/try/web/incremental_compilation_update_test.dart
index 9ce598642fd..ffea9182652 100644
--- a/tests/try/web/incremental_compilation_update_test.dart
+++ b/tests/try/web/incremental_compilation_update_test.dart
@@ -482,6 +482,60 @@ main() {
 """,
             const <String>['a', 'b', 'c']),
     ],
+
+    // Test that a newly instantiated class is handled.
+    const <ProgramResult>[
+        const ProgramResult(
+            r"""
+class A {
+  get name => 'A.m';
+
+  m() {
+    print('Called $name');
+  }
+}
+
+class B extends A {
+  get name => 'B.m';
+}
+
+var instance;
+main() {
+  if (instance == null) {
+    instance = new A();
+//   } else {
+//     instance = new B();
+  }
+  instance.m();
+}
+""",
+            const <String>['Called A.m']),
+        const ProgramResult(
+            r"""
+class A {
+  get name => 'A.m';
+
+  m() {
+    print('Called $name');
+  }
+}
+
+class B extends A {
+  get name => 'B.m';
+}
+
+var instance;
+main() {
+  if (instance == null) {
+    instance = new A();
+  } else {
+    instance = new B();
+  }
+  instance.m();
+}
+""",
+            const <String>['Called B.m']),
+    ],
 ];
 
 void main() {