diff --git a/components/style/servo/url.rs b/components/style/servo/url.rs
index b4821f21e66..91521c8a120 100644
--- a/components/style/servo/url.rs
+++ b/components/style/servo/url.rs
@@ -98,6 +98,18 @@ impl CssUrl {
             resolved: ServoUrl::parse(url).ok(),
         }
     }
+
+    /// Parses a URL request and records that the corresponding request needs to
+    /// be CORS-enabled.
+    ///
+    /// This is only for shape images and masks in Gecko, thus unimplemented for
+    /// now so somebody notices when trying to do so.
+    pub fn parse_with_cors_anonymous<'i, 't>(
+        _context: &ParserContext,
+        _input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        unimplemented!("Need to record somewhere that the request needs to be CORS-enabled")
+    }
 }
 
 impl Parse for CssUrl {
diff --git a/components/style/values/specified/image.rs b/components/style/values/specified/image.rs
index 2eabb452f02..1b080816e83 100644
--- a/components/style/values/specified/image.rs
+++ b/components/style/values/specified/image.rs
@@ -167,8 +167,11 @@ impl Image {
         })
     }
 
-    /// Provides an alternate method for parsing that associates the URL
-    /// with anonymous CORS headers.
+    /// Provides an alternate method for parsing that associates the URL with
+    /// anonymous CORS headers.
+    ///
+    /// FIXME(emilio): It'd be nicer for this to pass a `CorsMode` parameter to
+    /// a shared function instead.
     pub fn parse_with_cors_anonymous<'i, 't>(
         context: &ParserContext,
         input: &mut Parser<'i, 't>,