diff --git a/javatests/jsinterop/generator/externs/nullabletypes/BUILD b/javatests/jsinterop/generator/externs/nullabletypes/BUILD
new file mode 100644
index 0000000..749e028
--- /dev/null
+++ b/javatests/jsinterop/generator/externs/nullabletypes/BUILD
@@ -0,0 +1,17 @@
+load(
+    "//javatests/jsinterop/generator:jsinterop_generator_test.bzl",
+    "jsinterop_generator_test",
+)
+
+package(
+    default_applicable_licenses = ["//:license"],
+    licenses = ["notice"],
+)
+
+jsinterop_generator_test(
+    name = "nullabletypes",
+    srcs = ["nullabletypes.js"],
+    expected_output = glob([
+        "*.java.txt",
+    ]),
+)
diff --git a/javatests/jsinterop/generator/externs/nullabletypes/ClassWithNullableRefs.java.txt b/javatests/jsinterop/generator/externs/nullabletypes/ClassWithNullableRefs.java.txt
new file mode 100644
index 0000000..05c9fd8
--- /dev/null
+++ b/javatests/jsinterop/generator/externs/nullabletypes/ClassWithNullableRefs.java.txt
@@ -0,0 +1,196 @@
+package jsinterop.generator.externs.nullabletypes;
+
+import jsinterop.annotations.JsFunction;
+import jsinterop.annotations.JsOverlay;
+import jsinterop.annotations.JsPackage;
+import jsinterop.annotations.JsProperty;
+import jsinterop.annotations.JsType;
+import jsinterop.base.Js;
+import jsinterop.base.JsPropertyMap;
+
+@JsType(isNative = true, namespace = JsPackage.GLOBAL)
+public class ClassWithNullableRefs {
+  @JsType(isNative = true, name = "?", namespace = JsPackage.GLOBAL)
+  public interface AnonymousUnionTypeWithNullUnionType {
+    @JsOverlay
+    static ClassWithNullableRefs.AnonymousUnionTypeWithNullUnionType of(Object o) {
+      return Js.cast(o);
+    }
+
+    @JsOverlay
+    default double asDouble() {
+      return Js.asDouble(this);
+    }
+
+    @JsOverlay
+    default String asString() {
+      return Js.asString(this);
+    }
+
+    @JsOverlay
+    default boolean isDouble() {
+      return (Object) this instanceof Double;
+    }
+
+    @JsOverlay
+    default boolean isString() {
+      return (Object) this instanceof String;
+    }
+  }
+
+  @JsFunction
+  public interface NullableAnonymousFunctionTypeRefFn {
+    boolean onInvoke(String p0);
+  }
+
+  @JsType(isNative = true, name = "?", namespace = JsPackage.GLOBAL)
+  public interface NullableAnonymousRecordRefFieldType {
+    @JsOverlay
+    static ClassWithNullableRefs.NullableAnonymousRecordRefFieldType create() {
+      return Js.uncheckedCast(JsPropertyMap.of());
+    }
+
+    @JsProperty
+    String getBar();
+
+    @JsProperty
+    double getFoo();
+
+    @JsProperty
+    void setBar(String bar);
+
+    @JsProperty
+    void setFoo(double foo);
+  }
+
+  @JsType(isNative = true, name = "?", namespace = JsPackage.GLOBAL)
+  public interface NullableAnonymousUnionTypeRef2UnionType {
+    @JsOverlay
+    static ClassWithNullableRefs.NullableAnonymousUnionTypeRef2UnionType of(Object o) {
+      return Js.cast(o);
+    }
+
+    @JsOverlay
+    default double asDouble() {
+      return Js.asDouble(this);
+    }
+
+    @JsOverlay
+    default String asString() {
+      return Js.asString(this);
+    }
+
+    @JsOverlay
+    default boolean isDouble() {
+      return (Object) this instanceof Double;
+    }
+
+    @JsOverlay
+    default boolean isString() {
+      return (Object) this instanceof String;
+    }
+  }
+
+  @JsType(isNative = true, name = "?", namespace = JsPackage.GLOBAL)
+  public interface NullableAnonymousUnionTypeRefUnionType {
+    @JsOverlay
+    static ClassWithNullableRefs.NullableAnonymousUnionTypeRefUnionType of(Object o) {
+      return Js.cast(o);
+    }
+
+    @JsOverlay
+    default double asDouble() {
+      return Js.asDouble(this);
+    }
+
+    @JsOverlay
+    default String asString() {
+      return Js.asString(this);
+    }
+
+    @JsOverlay
+    default boolean isDouble() {
+      return (Object) this instanceof Double;
+    }
+
+    @JsOverlay
+    default boolean isString() {
+      return (Object) this instanceof String;
+    }
+  }
+
+  @JsType(isNative = true, name = "?", namespace = JsPackage.GLOBAL)
+  public interface NullableUnionTypeRefUnionType {
+    @JsOverlay
+    static ClassWithNullableRefs.NullableUnionTypeRefUnionType of(Object o) {
+      return Js.cast(o);
+    }
+
+    @JsOverlay
+    default double asDouble() {
+      return Js.asDouble(this);
+    }
+
+    @JsOverlay
+    default String asString() {
+      return Js.asString(this);
+    }
+
+    @JsOverlay
+    default boolean isDouble() {
+      return (Object) this instanceof Double;
+    }
+
+    @JsOverlay
+    default boolean isString() {
+      return (Object) this instanceof String;
+    }
+  }
+
+  @JsType(isNative = true, name = "?", namespace = JsPackage.GLOBAL)
+  public interface UnionTypeWithNullRefUnionType {
+    @JsOverlay
+    static ClassWithNullableRefs.UnionTypeWithNullRefUnionType of(Object o) {
+      return Js.cast(o);
+    }
+
+    @JsOverlay
+    default double asDouble() {
+      return Js.asDouble(this);
+    }
+
+    @JsOverlay
+    default String asString() {
+      return Js.asString(this);
+    }
+
+    @JsOverlay
+    default boolean isDouble() {
+      return (Object) this instanceof Double;
+    }
+
+    @JsOverlay
+    default boolean isString() {
+      return (Object) this instanceof String;
+    }
+  }
+
+  public ClassWithNullableRefs.AnonymousUnionTypeWithNullUnionType anonymousUnionTypeWithNull;
+  public ClassWithNullableRefs.NullableAnonymousFunctionTypeRefFn nullableAnonymousFunctionTypeRef;
+  public ClassWithNullableRefs.NullableAnonymousRecordRefFieldType nullableAnonymousRecordRef;
+  public ClassWithNullableRefs.NullableAnonymousUnionTypeRefUnionType nullableAnonymousUnionTypeRef;
+  public ClassWithNullableRefs.NullableAnonymousUnionTypeRef2UnionType
+      nullableAnonymousUnionTypeRef2;
+  public SimpleEnum nullableEnumRef;
+  public NullableFunctionType nullableFunctionTypeRef;
+  public SimpleInterface nullableInterfaceRef;
+  public double nullableNumber;
+  public SimpleRecord nullableRecordRef;
+  public String nullableString;
+  public NullableTypeDefOfRecord nullableTypeDefOfRecordRef;
+  public ClassWithNullableRefs.NullableUnionTypeRefUnionType nullableUnionTypeRef;
+  public SimpleClass simpleClassRef;
+  public ClassWithNullableRefs.UnionTypeWithNullRefUnionType unionTypeWithNullRef;
+
+  public native SimpleRecord methodWithNullableParam(SimpleInterface foo);
+}
diff --git a/javatests/jsinterop/generator/externs/nullabletypes/NullableFunctionType.java.txt b/javatests/jsinterop/generator/externs/nullabletypes/NullableFunctionType.java.txt
new file mode 100644
index 0000000..c133ac5
--- /dev/null
+++ b/javatests/jsinterop/generator/externs/nullabletypes/NullableFunctionType.java.txt
@@ -0,0 +1,8 @@
+package jsinterop.generator.externs.nullabletypes;
+
+import jsinterop.annotations.JsFunction;
+
+@JsFunction
+public interface NullableFunctionType {
+  boolean onInvoke(String p0);
+}
diff --git a/javatests/jsinterop/generator/externs/nullabletypes/NullableTypeDefOfRecord.java.txt b/javatests/jsinterop/generator/externs/nullabletypes/NullableTypeDefOfRecord.java.txt
new file mode 100644
index 0000000..fcd6c22
--- /dev/null
+++ b/javatests/jsinterop/generator/externs/nullabletypes/NullableTypeDefOfRecord.java.txt
@@ -0,0 +1,28 @@
+package jsinterop.generator.externs.nullabletypes;
+
+import jsinterop.annotations.JsOverlay;
+import jsinterop.annotations.JsPackage;
+import jsinterop.annotations.JsProperty;
+import jsinterop.annotations.JsType;
+import jsinterop.base.Js;
+import jsinterop.base.JsPropertyMap;
+
+@JsType(isNative = true, namespace = JsPackage.GLOBAL)
+public interface NullableTypeDefOfRecord {
+  @JsOverlay
+  static NullableTypeDefOfRecord create() {
+    return Js.uncheckedCast(JsPropertyMap.of());
+  }
+
+  @JsProperty
+  String getBar();
+
+  @JsProperty
+  double getFoo();
+
+  @JsProperty
+  void setBar(String bar);
+
+  @JsProperty
+  void setFoo(double foo);
+}
diff --git a/javatests/jsinterop/generator/externs/nullabletypes/SimpleClass.java.txt b/javatests/jsinterop/generator/externs/nullabletypes/SimpleClass.java.txt
new file mode 100644
index 0000000..b6e2bce
--- /dev/null
+++ b/javatests/jsinterop/generator/externs/nullabletypes/SimpleClass.java.txt
@@ -0,0 +1,7 @@
+package jsinterop.generator.externs.nullabletypes;
+
+import jsinterop.annotations.JsPackage;
+import jsinterop.annotations.JsType;
+
+@JsType(isNative = true, namespace = JsPackage.GLOBAL)
+public class SimpleClass {}
diff --git a/javatests/jsinterop/generator/externs/nullabletypes/SimpleEnum.java.txt b/javatests/jsinterop/generator/externs/nullabletypes/SimpleEnum.java.txt
new file mode 100644
index 0000000..1bc5dbe
--- /dev/null
+++ b/javatests/jsinterop/generator/externs/nullabletypes/SimpleEnum.java.txt
@@ -0,0 +1,10 @@
+package jsinterop.generator.externs.nullabletypes;
+
+import jsinterop.annotations.JsEnum;
+import jsinterop.annotations.JsPackage;
+
+@JsEnum(isNative = true, namespace = JsPackage.GLOBAL)
+public enum SimpleEnum {
+  A,
+  B;
+}
diff --git a/javatests/jsinterop/generator/externs/nullabletypes/SimpleInterface.java.txt b/javatests/jsinterop/generator/externs/nullabletypes/SimpleInterface.java.txt
new file mode 100644
index 0000000..e71ba7f
--- /dev/null
+++ b/javatests/jsinterop/generator/externs/nullabletypes/SimpleInterface.java.txt
@@ -0,0 +1,7 @@
+package jsinterop.generator.externs.nullabletypes;
+
+import jsinterop.annotations.JsPackage;
+import jsinterop.annotations.JsType;
+
+@JsType(isNative = true, namespace = JsPackage.GLOBAL)
+public interface SimpleInterface {}
diff --git a/javatests/jsinterop/generator/externs/nullabletypes/SimpleRecord.java.txt b/javatests/jsinterop/generator/externs/nullabletypes/SimpleRecord.java.txt
new file mode 100644
index 0000000..666333b
--- /dev/null
+++ b/javatests/jsinterop/generator/externs/nullabletypes/SimpleRecord.java.txt
@@ -0,0 +1,7 @@
+package jsinterop.generator.externs.nullabletypes;
+
+import jsinterop.annotations.JsPackage;
+import jsinterop.annotations.JsType;
+
+@JsType(isNative = true, namespace = JsPackage.GLOBAL)
+public interface SimpleRecord {}
diff --git a/javatests/jsinterop/generator/externs/nullabletypes/nullabletypes.js b/javatests/jsinterop/generator/externs/nullabletypes/nullabletypes.js
new file mode 100644
index 0000000..6d00bfd
--- /dev/null
+++ b/javatests/jsinterop/generator/externs/nullabletypes/nullabletypes.js
@@ -0,0 +1,151 @@
+
+// Copyright 2024 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+/**
+ * @fileoverview Test nested classes conversion.
+ * @externs
+ */
+
+/**
+ * @constructor
+ */
+function SimpleClass() {}
+
+/**
+ * @record
+ */
+function SimpleRecord() {};
+
+/**
+ * @interface
+ */
+function SimpleInterface() {}
+
+/**
+ * @enum {string}
+ */
+var SimpleEnum = {A: 'A', B: 'B'};
+
+/**
+ * @typedef {?function(string):boolean}
+ */
+var NullableFunctionType;
+
+/**
+ * @typedef {?string|number}
+ */
+var NullableUnionType;
+
+/**
+ * @typedef {null|string|number}
+ */
+var UnionTypeWithNull;
+
+/**
+ * @typedef {?{
+ *      foo: number,
+ *      bar: string
+ *      }}
+ */
+var NullableTypeDefOfRecord;
+
+/**
+ * @constructor
+ */
+function ClassWithNullableRefs() {}
+
+/**
+@type {?SimpleClass}
+ */
+ClassWithNullableRefs.prototype.simpleClassRef;
+
+/**
+ * @type {?SimpleRecord}
+ */
+ClassWithNullableRefs.prototype.nullableRecordRef;
+
+/**
+ * @type {?SimpleInterface}
+ */
+ClassWithNullableRefs.prototype.nullableInterfaceRef;
+
+/**
+ * @type {?SimpleEnum}
+ */
+ClassWithNullableRefs.prototype.nullableEnumRef;
+
+/**
+ * @param {?SimpleInterface} foo
+ * @return {?SimpleRecord}
+ */
+ClassWithNullableRefs.prototype.methodWithNullableParam = function(foo) {};
+
+/**
+ * @type {?string|number}
+ */
+ClassWithNullableRefs.prototype.nullableAnonymousUnionTypeRef;
+
+/**
+ * @type {?(string|number)}
+ */
+ClassWithNullableRefs.prototype.nullableAnonymousUnionTypeRef2;
+
+/**
+ * @type {?function(string):boolean}
+ */
+ClassWithNullableRefs.prototype.nullableAnonymousFunctionTypeRef;
+
+/**
+ * @type {?{
+ *      foo: number,
+ *      bar: string
+ *      }}
+ */
+ClassWithNullableRefs.prototype.nullableAnonymousRecordRef;
+
+/**
+ * @type {NullableUnionType}
+ */
+ClassWithNullableRefs.prototype.nullableUnionTypeRef;
+
+/**
+ * @type {NullableFunctionType}
+ */
+ClassWithNullableRefs.prototype.nullableFunctionTypeRef;
+
+/**
+ * @type {UnionTypeWithNull}
+ */
+ClassWithNullableRefs.prototype.unionTypeWithNullRef;
+
+/**
+ * @type {null|string|number}
+ */
+ClassWithNullableRefs.prototype.anonymousUnionTypeWithNull;
+
+/**
+ * @type {NullableTypeDefOfRecord}
+ */
+ClassWithNullableRefs.prototype.nullableTypeDefOfRecordRef;
+
+/**
+ * @type {?number}
+ */
+ClassWithNullableRefs.prototype.nullableNumber;
+
+/**
+ * @type {?string}
+ */
+ClassWithNullableRefs.prototype.nullableString;