diff --git a/src/components/script/dom/bindings/codegen/CodegenRust.py b/src/components/script/dom/bindings/codegen/CodegenRust.py
index 14d558958dc..40c9e3b87ba 100644
--- a/src/components/script/dom/bindings/codegen/CodegenRust.py
+++ b/src/components/script/dom/bindings/codegen/CodegenRust.py
@@ -518,7 +518,7 @@ def getJSToNativeConversionTemplate(type, descriptorProvider, failureCode=None,
         if not isinstance(defaultValue, IDLNullValue):
             raise TypeError("Can't handle non-null default value here")
 
-        assert type.nullable() or type.isAny() or type.isDictionary()
+        assert type.nullable() or type.isDictionary()
         return nullValue
 
     # A helper function for wrapping up the template body for
@@ -752,7 +752,17 @@ def getJSToNativeConversionTemplate(type, descriptorProvider, failureCode=None,
         assert not isEnforceRange and not isClamp
 
         declType = CGGeneric("JSVal")
-        return handleOptional("${val}", declType, handleDefaultNull("NullValue()"))
+
+        if defaultValue is None:
+            default = None
+        elif isinstance(defaultValue, IDLNullValue):
+            default = "NullValue()"
+        elif isinstance(defaultValue, IDLUndefinedValue):
+            default = "UndefinedValue()"
+        else:
+            raise TypeError("Can't handle non-null, non-undefined default value here")
+
+        return handleOptional("${val}", declType, default)
 
     if type.isObject():
         raise TypeError("Can't handle object arguments yet")
diff --git a/src/components/script/dom/testbinding.rs b/src/components/script/dom/testbinding.rs
index 852b7443418..984c67ee3e0 100644
--- a/src/components/script/dom/testbinding.rs
+++ b/src/components/script/dom/testbinding.rs
@@ -180,7 +180,7 @@ pub trait TestBindingMethods {
     fn PassOptionalInterface(&self, _: Option<JSRef<Blob>>) {}
     fn PassOptionalUnion(&self, _: Option<HTMLElementOrLong>) {}
     fn PassOptionalUnion2(&self, _: Option<EventOrString>) {}
-    fn PassOptionalAny(&self, _: *mut JSContext, _: Option<JSVal>) {}
+    fn PassOptionalAny(&self, _: *mut JSContext, _: JSVal) {}
 
     fn PassOptionalNullableBoolean(&self, _: Option<Option<bool>>) {}
     fn PassOptionalNullableByte(&self, _: Option<Option<i8>>) {}