diff --git a/components/style/properties/longhand/ui.mako.rs b/components/style/properties/longhand/ui.mako.rs
index c33f41a654e..2e3f52d12be 100644
--- a/components/style/properties/longhand/ui.mako.rs
+++ b/components/style/properties/longhand/ui.mako.rs
@@ -49,12 +49,10 @@ ${helpers.single_keyword("-moz-window-shadow", "none default menu tooltip sheet"
                    spec="None (Nonstandard Firefox-only property)">
     use std::fmt;
     use style_traits::ToCss;
-    use values::computed::ComputedValueAsSpecified;
-
 
     pub mod computed_value {
-        #[derive(Clone, Copy, Debug, PartialEq)]
         #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+        #[derive(Clone, Copy, Debug, PartialEq, ToComputedValue)]
         pub struct T(pub bool);
     }
 
@@ -76,8 +74,6 @@ ${helpers.single_keyword("-moz-window-shadow", "none default menu tooltip sheet"
         computed_value::T(false)
     }
 
-    impl ComputedValueAsSpecified for SpecifiedValue {}
-
     pub fn parse<'i, 't>(_context: &ParserContext, input: &mut Parser<'i, 't>)
                          -> Result<SpecifiedValue, ParseError<'i>> {
         match input.expect_integer()? {