diff --git a/components/style/values/specified/box.rs b/components/style/values/specified/box.rs
index 059188f824d..3caee1e7f08 100644
--- a/components/style/values/specified/box.rs
+++ b/components/style/values/specified/box.rs
@@ -6,6 +6,7 @@
 
 use Atom;
 use cssparser::Parser;
+use custom_properties::Name as CustomPropertyName;
 use parser::{Parse, ParserContext};
 use properties::{LonghandId, ShorthandId, PropertyId, PropertyFlags, PropertyDeclarationId};
 use selectors::parser::SelectorParseErrorKind;
@@ -724,7 +725,7 @@ pub enum TransitionProperty {
     /// A longhand transitionable property.
     Longhand(LonghandId),
     /// A custom property.
-    Custom(Atom),
+    Custom(CustomPropertyName),
     /// Unrecognized property which could be any non-transitionable, custom property, or
     /// unknown property.
     Unsupported(CustomIdent),