diff --git a/test/com/google/javascript/jscomp/IntegrationTest.java b/test/com/google/javascript/jscomp/IntegrationTest.java
index 350f734785b..48cd886f61c 100644
--- a/test/com/google/javascript/jscomp/IntegrationTest.java
+++ b/test/com/google/javascript/jscomp/IntegrationTest.java
@@ -572,14 +572,46 @@ public void testWindowIsTypedEs6() {
         TypeValidator.TYPE_MISMATCH_WARNING);
   }
 
-  public void testConstPolymerNotAllowed() {
+  private void addPolymerExterns() {
+    ImmutableList.Builder<SourceFile> externsList = ImmutableList.builder();
+    externsList.addAll(externs);
+    externsList.add(
+        SourceFile.fromCode(
+            "polymer_externs.js",
+            lines(
+                "/** @return {function(new: PolymerElement)} */",
+                "var Polymer = function(descriptor) {};",
+                "",
+                "/** @constructor @extends {HTMLElement} */",
+                "var PolymerElement = function() {};",  // Polymer 1
+                "",
+                "/** @constructor @extends {HTMLElement} */",
+                "Polymer.Element = function() {};",  // Polymer 2
+                "")));
+    externs = externsList.build();
+  }
+
+  public void testPolymer1() {
     CompilerOptions options = createCompilerOptions();
     options.setPolymerVersion(1);
-    options.setLanguageIn(LanguageMode.ECMASCRIPT_2015);
+    options.setWarningLevel(DiagnosticGroups.CHECK_TYPES, CheckLevel.ERROR);
+    options.setLanguageIn(LanguageMode.ECMASCRIPT_2017);
     options.setLanguageOut(LanguageMode.ECMASCRIPT5);
+    addPolymerExterns();
 
-    externs = ImmutableList.of(SourceFile.fromCode("<externs>",
-        "var Polymer = function() {}; var PolymerElement = function() {};"));
+    test(
+        options,
+        "var XFoo = Polymer({ is: 'x-foo' });",
+        "var XFoo=function(){};XFoo=Polymer({is:'x-foo'})");
+  }
+
+  public void testConstPolymerElementNotAllowed() {
+    CompilerOptions options = createCompilerOptions();
+    options.setPolymerVersion(1);
+    options.setWarningLevel(DiagnosticGroups.CHECK_TYPES, CheckLevel.ERROR);
+    options.setLanguageIn(LanguageMode.ECMASCRIPT_2017);
+    options.setLanguageOut(LanguageMode.ECMASCRIPT5);
+    addPolymerExterns();
 
     test(
         options,
@@ -587,6 +619,49 @@ public void testConstPolymerNotAllowed() {
         PolymerPassErrors.POLYMER_INVALID_DECLARATION);
   }
 
+  public void testPolymer2_nti() {
+    CompilerOptions options = createCompilerOptions();
+    options.setPolymerVersion(2);
+    options.setNewTypeInference(true);
+    options.setWarningLevel(DiagnosticGroups.CHECK_TYPES, CheckLevel.ERROR);
+    options.declaredGlobalExternsOnWindow = true;
+    options.setLanguageIn(LanguageMode.ECMASCRIPT_2017);
+    options.setLanguageOut(LanguageMode.ECMASCRIPT5);
+    addPolymerExterns();
+
+    Compiler compiler = compile(
+        options,
+        lines(
+            "class XFoo extends PolymerElement {",
+            "  get is() { return 'x-foo'; }",
+            "  static get properties() { return { bar: Boolean, }; }",
+            "}"));
+    assertThat(compiler.getErrors()).isEmpty();
+    assertThat(compiler.getWarnings()).isEmpty();
+  }
+
+  public void testPolymer2_oti() {
+    CompilerOptions options = createCompilerOptions();
+    options.setPolymerVersion(2);
+    options.setNewTypeInference(false);
+    options.setWarningLevel(DiagnosticGroups.CHECK_TYPES, CheckLevel.ERROR);
+    options.declaredGlobalExternsOnWindow = true;
+    options.setLanguageIn(LanguageMode.ECMASCRIPT_2017);
+    options.setLanguageOut(LanguageMode.ECMASCRIPT5);
+    addPolymerExterns();
+
+    // TODO(b/74549003): Fix this so that OTI doesn't report an error.
+    test(
+        options,
+        lines(
+            "class XFoo extends Polymer.Element {",
+            "  get is() { return 'x-foo'; }",
+            "  static get properties() { return {}; }",
+            "}"),
+        // Bad type annotation. Unknown type Polymer.ElementProperties
+        RhinoErrorReporter.UNRECOGNIZED_TYPE_ERROR);
+  }
+
   public void testPreservedForwardDeclare() {
     CompilerOptions options = createCompilerOptions();
     WarningLevel.VERBOSE.setOptionsForWarningLevel(options);
diff --git a/test/com/google/javascript/jscomp/IntegrationTestCase.java b/test/com/google/javascript/jscomp/IntegrationTestCase.java
index 3df2cca6cd0..4ed24b4809d 100644
--- a/test/com/google/javascript/jscomp/IntegrationTestCase.java
+++ b/test/com/google/javascript/jscomp/IntegrationTestCase.java
@@ -188,6 +188,7 @@ abstract class IntegrationTestCase extends TestCase {
                   "Object.seal;",
                   "Object.defineProperties;",
                   "Object.defineProperty;",
+                  "Object.getOwnPropertyDescriptor;",
                   "",
                   "Object.prototype;",
                   "",
@@ -271,6 +272,9 @@ abstract class IntegrationTestCase extends TestCase {
                   "function IThenable() {}",
                   "",
                   "IThenable.prototype.then = function(callback) {};",
+                  "",
+                  "/** @constructor */",
+                  "var HTMLElement = function() {};",
                   "")));
 
   protected List<SourceFile> externs = DEFAULT_EXTERNS;