diff --git a/dev/core/src/com/google/gwt/dev/jjs/impl/JsInteropRestrictionChecker.java b/dev/core/src/com/google/gwt/dev/jjs/impl/JsInteropRestrictionChecker.java
index f204bd06de..23f52db12f 100644
--- a/dev/core/src/com/google/gwt/dev/jjs/impl/JsInteropRestrictionChecker.java
+++ b/dev/core/src/com/google/gwt/dev/jjs/impl/JsInteropRestrictionChecker.java
@@ -285,7 +285,7 @@ private void checkIllegalOverrides(JMember member) {
   }
 
   private void checkJsOverlay(JMember member) {
-    if (member.getEnclosingType().isJsoType()) {
+    if (member.getEnclosingType().isJsoType() || member.isSynthetic()) {
       return;
     }
 
diff --git a/dev/core/test/com/google/gwt/dev/jjs/impl/JsInteropRestrictionCheckerTest.java b/dev/core/test/com/google/gwt/dev/jjs/impl/JsInteropRestrictionCheckerTest.java
index f7991aae9c..f1546d5c64 100644
--- a/dev/core/test/com/google/gwt/dev/jjs/impl/JsInteropRestrictionCheckerTest.java
+++ b/dev/core/test/com/google/gwt/dev/jjs/impl/JsInteropRestrictionCheckerTest.java
@@ -1613,7 +1613,7 @@ public void testNativeJsTypeInterfaceExtendsNonJsTypeFails() {
         "Line 6: Native JsType ''EntryPoint.Buggy'' can only extend native JsType interfaces.");
   }
 
-  public void testNativeJsTypeInterfaceDefenderMethodsFails() {
+  public void testNativeJsTypeInterfaceDefaultMethodsFails() {
     addSnippetImport("jsinterop.annotations.JsType");
     addSnippetImport("jsinterop.annotations.JsOverlay");
     addSnippetClassDecl(
@@ -1626,6 +1626,11 @@ public void testNativeJsTypeInterfaceDefenderMethodsFails() {
         "@JsType(isNative=true) public interface Buggy extends Interface {",
         "  default void someMethod(){}",
         "  void someOtherMethod();",
+        "}",
+        "public static class SomeOtherClass implements Interface {",
+        "}",
+        "public static class ClassOverridingOverlayTransitively extends SomeOtherClass {",
+        "  public void someOtherMethod() {}",
         "}");
 
     assertBuggyFails(
@@ -1634,7 +1639,9 @@ public void testNativeJsTypeInterfaceDefenderMethodsFails() {
         "Line 12: Native JsType method 'void EntryPoint.Buggy.someMethod()' should be native "
             + "or abstract.",
         "Line 13: Method 'void EntryPoint.Buggy.someOtherMethod()' cannot override a JsOverlay"
-            + " method 'void EntryPoint.Interface.someOtherMethod()'.");
+            + " method 'void EntryPoint.Interface.someOtherMethod()'.",
+        "Line 18: Method 'void EntryPoint.ClassOverridingOverlayTransitively.someOtherMethod()' "
+            + "cannot override a JsOverlay method 'void EntryPoint.Interface.someOtherMethod()'.");
   }
 
   public void testJsOptionalSucceeds() throws Exception {
@@ -2190,13 +2197,28 @@ public void testNonJsTypeExtendingNativeJsTypeWithInstanceMethodSucceeds() throw
         "  public native void m(Object o);",
         "  public native void m(Object[] o);",
         "}",
-        "@JsType public static class Buggy extends Super {",
+        "public static class Buggy extends Super {",
         "  public void n(Object o) { }",
         "}");
 
     assertBuggySucceeds();
   }
 
+  public void testClassesExtendingNativeJsTypeInterfaceWithOverlaySucceeds() throws Exception {
+    addSnippetImport("jsinterop.annotations.JsOverlay");
+    addSnippetImport("jsinterop.annotations.JsType");
+    addSnippetClassDecl(
+        "@JsType(isNative=true) interface Super {",
+        "  @JsOverlay default void fun() {}",
+        "}",
+        "@JsType(isNative=true) abstract static class Buggy implements Super {",
+        "}",
+        "static class JavaSubclass implements Super {",
+        "}");
+
+    assertBuggySucceeds();
+  }
+
   public void testNonJsTypeExtendingNativeJsTypeWithInstanceMethodOverloadsFails() {
     addSnippetImport("jsinterop.annotations.JsType");
     addSnippetClassDecl(
diff --git a/user/test-super/com/google/gwt/dev/jjs/super/com/google/gwt/dev/jjs/test/Java8Test.java b/user/test-super/com/google/gwt/dev/jjs/super/com/google/gwt/dev/jjs/test/Java8Test.java
index 8d896cb282..6684445a32 100644
--- a/user/test-super/com/google/gwt/dev/jjs/super/com/google/gwt/dev/jjs/test/Java8Test.java
+++ b/user/test-super/com/google/gwt/dev/jjs/super/com/google/gwt/dev/jjs/test/Java8Test.java
@@ -26,6 +26,8 @@
 
 import jsinterop.annotations.JsFunction;
 import jsinterop.annotations.JsOverlay;
+import jsinterop.annotations.JsPackage;
+import jsinterop.annotations.JsProperty;
 import jsinterop.annotations.JsType;
 
 /**
@@ -1672,10 +1674,34 @@ public static String m() {
       return null;
     }
   }
-   // Regression test for bug: #9426.
+
+  // Regression test for bug: #9426.
   public void testCorrectNaming() {
     Function<String> f = ClassWithAVeryLoooooooooooooooooooooooooooooooooooongName::m;
     assertNotNull(f);
   }
+
+  @JsType(isNative = true)
+  interface InterfaceWithOverlay {
+
+    @JsProperty
+    int getLength();
+
+    @JsOverlay
+    default int len() {
+      return this.getLength();
+    }
+  }
+
+  @JsType(isNative = true, name = "Object", namespace = JsPackage.GLOBAL)
+  static abstract class SubclassImplementingInterfaceWithOverlay implements InterfaceWithOverlay {
+  }
+
+  // Regression test for bug: #9440
+  public void testInterfaceWithOverlayAndNativeSubclass() {
+    SubclassImplementingInterfaceWithOverlay object =
+        (SubclassImplementingInterfaceWithOverlay) (Object) new int[]{1, 2, 3};
+    assertEquals(3, object.len());
+  }
 }
 
diff --git a/user/test/com/google/gwt/dev/jjs/test/Java8Test.java b/user/test/com/google/gwt/dev/jjs/test/Java8Test.java
index ff90ce9057..3cf89d1b34 100644
--- a/user/test/com/google/gwt/dev/jjs/test/Java8Test.java
+++ b/user/test/com/google/gwt/dev/jjs/test/Java8Test.java
@@ -308,6 +308,10 @@ public void testCorrectNaming() {
     assertFalse(isGwtSourceLevel8());
   }
 
+  public void testInterfaceWithOverlayAndNativeSubclass() {
+    assertFalse(isGwtSourceLevel8());
+  }
+
   private boolean isGwtSourceLevel8() {
     return JUnitShell.getCompilerOptions().getSourceLevel().compareTo(SourceLevel.JAVA8) >= 0;
   }