diff --git a/src/components/script/dom/bindings/codegen/CodegenRust.py b/src/components/script/dom/bindings/codegen/CodegenRust.py
index af9a39313da..bbdd6b9420e 100644
--- a/src/components/script/dom/bindings/codegen/CodegenRust.py
+++ b/src/components/script/dom/bindings/codegen/CodegenRust.py
@@ -1063,13 +1063,19 @@ for (uint32_t i = 0; i < length; ++i) {
                 assert(type.nullable())
                 return handleDefault(conversionCode,
                                      "%s.SetNull()" % varName)
-            return handleDefault(
-                conversionCode,
-                ("static data: [u8, ..%s] = [ %s ];\n"
-                 "%s = str::from_utf8(data).to_owned()" %
-                 (len(defaultValue.value) + 1,
-                  ", ".join(["'" + char + "' as u8" for char in defaultValue.value] + ["0"]),
-                  varName)))
+
+            value = "str::from_utf8(data).to_owned()"
+            if type.nullable():
+                value = "Some(%s)" % value
+
+            default = (
+                "static data: [u8, ..%s] = [ %s ];\n"
+                "%s = %s" %
+                (len(defaultValue.value) + 1,
+                 ", ".join(["'" + char + "' as u8" for char in defaultValue.value] + ["0"]),
+                 varName, value))
+
+            return handleDefault(conversionCode, default)
 
         if isMember:
             # We have to make a copy, because our jsval may well not
diff --git a/src/components/script/dom/testbinding.rs b/src/components/script/dom/testbinding.rs
index 1df1f97e606..2d0d3fc58bb 100644
--- a/src/components/script/dom/testbinding.rs
+++ b/src/components/script/dom/testbinding.rs
@@ -134,7 +134,7 @@ impl TestBinding {
     pub fn PassOptionalNullableUnsignedLongLongWithNonNullDefault(&self, _: Option<u64>) {}
     // pub fn PassOptionalNullableFloatWithNonNullDefault(&self, _: Option<f32>) {}
     // pub fn PassOptionalNullableDoubleWithNonNullDefault(&self, _: Option<f64>) {}
-    // pub fn PassOptionalNullableStringWithNonNullDefault(&self, _: Option<DOMString>) {}
+    pub fn PassOptionalNullableStringWithNonNullDefault(&self, _: Option<DOMString>) {}
 }
 
 impl Reflectable for TestBinding {
diff --git a/src/components/script/dom/webidls/TestBinding.webidl b/src/components/script/dom/webidls/TestBinding.webidl
index 5c0420d5160..ae655949cde 100644
--- a/src/components/script/dom/webidls/TestBinding.webidl
+++ b/src/components/script/dom/webidls/TestBinding.webidl
@@ -94,5 +94,5 @@ interface TestBinding {
   void passOptionalNullableUnsignedLongLongWithNonNullDefault(optional unsigned long long? arg = 7);
   // void passOptionalNullableFloatWithNonNullDefault(optional float? arg = 0.0);
   // void passOptionalNullableDoubleWithNonNullDefault(optional double? arg = 0.0);
-  // void passOptionalNullableStringWithNonNullDefault(optional DOMString? arg = "");
+  void passOptionalNullableStringWithNonNullDefault(optional DOMString? arg = "");
 };