diff --git a/components/style/properties/data.py b/components/style/properties/data.py
index 8db09e6fe81..eb1706e691e 100644
--- a/components/style/properties/data.py
+++ b/components/style/properties/data.py
@@ -140,7 +140,7 @@ class Longhand(object):
                  need_clone=False, need_index=False, gecko_ffi_name=None, depend_on_viewport_size=False,
                  allowed_in_keyframe_block=True, complex_color=False, cast_type='u8',
                  has_uncacheable_values=False, logical=False, alias=None, extra_prefixes=None, boxed=False,
-                 flags=None, allowed_in_page_rule=False, allow_quirks=False):
+                 flags=None, allowed_in_page_rule=False, allow_quirks=False, vector=False):
         self.name = name
         if not spec:
             raise TypeError("Spec should be specified for %s" % name)
@@ -167,6 +167,7 @@ class Longhand(object):
         self.flags = flags.split() if flags else []
         self.allowed_in_page_rule = arg_to_bool(allowed_in_page_rule)
         self.allow_quirks = allow_quirks
+        self.is_vector = vector
 
         # https://drafts.csswg.org/css-animations/#keyframes
         # > The <declaration-list> inside of <keyframe-block> accepts any CSS property
diff --git a/components/style/properties/helpers.mako.rs b/components/style/properties/helpers.mako.rs
index b69057f916c..65478210d4e 100644
--- a/components/style/properties/helpers.mako.rs
+++ b/components/style/properties/helpers.mako.rs
@@ -74,7 +74,7 @@
 </%doc>
 <%def name="vector_longhand(name, gecko_only=False, allow_empty=False,
             delegate_animate=False, space_separated_allowed=False, **kwargs)">
-    <%call expr="longhand(name, **kwargs)">
+    <%call expr="longhand(name, vector=True, **kwargs)">
         % if not gecko_only:
             use smallvec::SmallVec;
             use std::fmt;
@@ -103,6 +103,8 @@
                 pub use super::single_value::computed_value as single_value;
                 pub use self::single_value::T as SingleComputedValue;
                 use smallvec::SmallVec;
+                use values::computed::ComputedVecIter;
+
                 /// The computed value, effectively a list of single values.
                 #[derive(Debug, Clone, PartialEq)]
                 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
@@ -129,6 +131,8 @@
                         }
                     }
                 % endif
+
+                pub type Iter<'a, 'cx, 'cx_a> = ComputedVecIter<'a, 'cx, 'cx_a, super::single_value::SpecifiedValue>;
             }
 
             impl ToCss for computed_value::T {
@@ -212,12 +216,18 @@
 
             pub use self::single_value::SpecifiedValue as SingleSpecifiedValue;
 
+            impl SpecifiedValue {
+                pub fn compute_iter<'a, 'cx, 'cx_a>(&'a self, context: &'cx Context<'cx_a>) -> computed_value::Iter<'a, 'cx, 'cx_a> {
+                    computed_value::Iter::new(context, &self.0)
+                }
+            }
+
             impl ToComputedValue for SpecifiedValue {
                 type ComputedValue = computed_value::T;
 
                 #[inline]
                 fn to_computed_value(&self, context: &Context) -> computed_value::T {
-                    computed_value::T(self.0.iter().map(|x| x.to_computed_value(context)).collect())
+                    computed_value::T(self.compute_iter(context).collect())
                 }
                 #[inline]
                 fn from_computed_value(computed: &computed_value::T) -> Self {
diff --git a/components/style/values/computed/mod.rs b/components/style/values/computed/mod.rs
index 19cc22edf27..12775a78218 100644
--- a/components/style/values/computed/mod.rs
+++ b/components/style/values/computed/mod.rs
@@ -100,6 +100,35 @@ impl<'a> Context<'a> {
     pub fn mutate_style(&mut self) -> &mut StyleBuilder<'a> { &mut self.style }
 }
 
+/// An iterator over a slice of computed values
+pub struct ComputedVecIter<'a, 'cx, 'cx_a: 'cx, S: ToComputedValue + 'a> {
+    cx: &'cx Context<'cx_a>,
+    values: &'a [S],
+}
+
+impl<'a, 'cx, 'cx_a: 'cx, S: ToComputedValue + 'a> ComputedVecIter<'a, 'cx, 'cx_a, S> {
+    /// Construct an iterator from a slice of specified values and a context
+    pub fn new(cx: &'cx Context<'cx_a>, values: &'a [S]) -> Self {
+        ComputedVecIter {
+            cx: cx,
+            values: values,
+        }
+    }
+}
+
+impl<'a, 'cx, 'cx_a: 'cx, S: ToComputedValue + 'a> Iterator for ComputedVecIter<'a, 'cx, 'cx_a, S> {
+    type Item = S::ComputedValue;
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some((next, rest)) = self.values.split_first() {
+            let ret = next.to_computed_value(self.cx);
+            self.values = rest;
+            Some(ret)
+        } else {
+            None
+        }
+    }
+}
+
 /// A trait to represent the conversion between computed and specified values.
 pub trait ToComputedValue {
     /// The computed value type we're going to be converted to.