diff --git a/ports/geckolib/lib.rs b/ports/geckolib/lib.rs
index 5a2a468d319..4b26a186c02 100644
--- a/ports/geckolib/lib.rs
+++ b/ports/geckolib/lib.rs
@@ -42,6 +42,7 @@ mod gecko_style_structs;
 pub mod glue;
 mod selector_impl;
 mod traversal;
+mod values;
 mod wrapper;
 
 // Generated from the properties.mako.rs template by build.rs
diff --git a/ports/geckolib/properties.mako.rs b/ports/geckolib/properties.mako.rs
index 7dd8f34013f..f18659c0ea0 100644
--- a/ports/geckolib/properties.mako.rs
+++ b/ports/geckolib/properties.mako.rs
@@ -28,6 +28,8 @@ use style::properties::{CascadePropertyFn, ServoComputedValues, ComputedValues};
 use style::properties::longhands;
 use style::properties::make_cascade_vec;
 use style::properties::style_struct_traits::*;
+use gecko_style_structs::{nsStyleUnion, nsStyleUnit};
+use values::ToGeckoStyleCoord;
 
 #[derive(Clone)]
 pub struct GeckoComputedValues {
@@ -196,6 +198,20 @@ def set_gecko_property(ffi_name, expr):
 % endif
 </%def>
 
+<%def name="impl_style_coord(ident, unit_ffi_name, union_ffi_name)">
+    fn set_${ident}(&mut self, v: longhands::${ident}::computed_value::T) {
+        v.to_gecko_style_coord(&mut self.gecko.${unit_ffi_name},
+                               &mut self.gecko.${union_ffi_name});
+    }
+    fn copy_${ident}_from(&mut self, other: &Self) {
+        use gecko_style_structs::nsStyleUnit::eStyleUnit_Calc;
+        assert!(self.gecko.${unit_ffi_name} != eStyleUnit_Calc,
+                "stylo: Can't yet handle refcounted Calc");
+        self.gecko.${unit_ffi_name} =  other.gecko.${unit_ffi_name};
+        self.gecko.${union_ffi_name} = other.gecko.${union_ffi_name};
+    }
+</%def>
+
 <%def name="impl_style_struct(style_struct)">
 impl ${style_struct.gecko_struct_name} {
     #[allow(dead_code, unused_variables)]
@@ -340,12 +356,7 @@ fn static_assert() {
 <% border_style_keyword = Keyword("border-style",
                                   "none solid double dotted dashed hidden groove ridge inset outset") %>
 
-<%
-skip_border_longhands = ""
-for side in SIDES:
-    skip_border_longhands += "border-{0}-style border-{0}-width ".format(side.ident)
-%>
-
+<% skip_border_longhands = " ".join(["border-{0}-style border-{0}-width ".format(x.ident) for x in SIDES]) %>
 <%self:impl_trait style_struct_name="Border"
                   skip_longhands="${skip_border_longhands}"
                   skip_additionals="*">
@@ -362,6 +373,26 @@ for side in SIDES:
     % endfor
 </%self:impl_trait>
 
+<% skip_margin_longhands = " ".join(["margin-%s" % x.ident for x in SIDES]) %>
+<%self:impl_trait style_struct_name="Margin"
+                  skip_longhands="${skip_margin_longhands}">
+
+    % for side in SIDES:
+    <% impl_style_coord("margin_%s" % side.ident,
+                        "mMargin.mUnits[%s]" % side.index, "mMargin.mValues[%s]" % side.index) %>
+    % endfor
+</%self:impl_trait>
+
+<% skip_padding_longhands = " ".join(["padding-%s" % x.ident for x in SIDES]) %>
+<%self:impl_trait style_struct_name="Padding"
+                  skip_longhands="${skip_padding_longhands}">
+
+    % for side in SIDES:
+    <% impl_style_coord("padding_%s" % side.ident,
+                        "mPadding.mUnits[%s]" % side.index, "mPadding.mValues[%s]" % side.index) %>
+    % endfor
+</%self:impl_trait>
+
 <%self:impl_trait style_struct_name="Outline"
                   skip_longhands="outline-style"
                   skip_additionals="*">
diff --git a/ports/geckolib/values.rs b/ports/geckolib/values.rs
new file mode 100644
index 00000000000..6d195519aeb
--- /dev/null
+++ b/ports/geckolib/values.rs
@@ -0,0 +1,46 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use gecko_style_structs::{nsStyleUnion, nsStyleUnit};
+use style::values::computed::{LengthOrPercentage, LengthOrPercentageOrAuto};
+
+pub trait ToGeckoStyleCoord {
+    fn to_gecko_style_coord(&self, unit: &mut nsStyleUnit, union: &mut nsStyleUnion);
+}
+
+impl ToGeckoStyleCoord for LengthOrPercentage {
+    fn to_gecko_style_coord(&self, unit: &mut nsStyleUnit, union: &mut nsStyleUnion) {
+        match *self {
+            LengthOrPercentage::Length(au) => {
+                *unit = nsStyleUnit::eStyleUnit_Coord;
+                unsafe { *union.mInt.as_mut() = au.0; }
+            },
+            LengthOrPercentage::Percentage(p) => {
+                *unit = nsStyleUnit::eStyleUnit_Percent;
+                unsafe { *union.mFloat.as_mut() = p; }
+            },
+            LengthOrPercentage::Calc(_) => unimplemented!(),
+        };
+    }
+}
+
+impl ToGeckoStyleCoord for LengthOrPercentageOrAuto {
+    fn to_gecko_style_coord(&self, unit: &mut nsStyleUnit, union: &mut nsStyleUnion) {
+        match *self {
+            LengthOrPercentageOrAuto::Length(au) => {
+                *unit = nsStyleUnit::eStyleUnit_Coord;
+                unsafe { *union.mInt.as_mut() = au.0; }
+            },
+            LengthOrPercentageOrAuto::Percentage(p) => {
+                *unit = nsStyleUnit::eStyleUnit_Percent;
+                unsafe { *union.mFloat.as_mut() = p; }
+            },
+            LengthOrPercentageOrAuto::Auto => {
+                *unit = nsStyleUnit::eStyleUnit_Auto;
+                unsafe { *union.mInt.as_mut() = 0; }
+            },
+            LengthOrPercentageOrAuto::Calc(_) => unimplemented!(),
+        };
+    }
+}