diff --git a/components/style/gecko/url.rs b/components/style/gecko/url.rs
index e5f1b32e04c9..a0bf3ff08293 100644
--- a/components/style/gecko/url.rs
+++ b/components/style/gecko/url.rs
@@ -19,8 +19,10 @@ use nsstring::nsCString;
 use servo_arc::Arc;
 use std::collections::HashMap;
 use std::fmt::{self, Write};
+use std::mem::ManuallyDrop;
 use std::sync::RwLock;
 use style_traits::{CssWriter, ParseError, ToCss};
+use to_shmem::{SharedMemoryBuilder, ToShmem};
 
 /// A CSS url() value for gecko.
 #[css(function = "url")]
@@ -138,6 +140,15 @@ pub enum URLValueSource {
     CORSMode(CORSMode),
 }
 
+impl ToShmem for URLValueSource {
+    fn to_shmem(&self, _builder: &mut SharedMemoryBuilder) -> ManuallyDrop<Self> {
+        ManuallyDrop::new(match self {
+            URLValueSource::URLValue(r) => URLValueSource::CORSMode(r.mCORSMode),
+            URLValueSource::CORSMode(c) => URLValueSource::CORSMode(*c),
+        })
+    }
+}
+
 /// A specified non-image `url()` value.
 #[derive(Clone, Debug, SpecifiedValueInfo, ToCss)]
 pub struct SpecifiedUrl {