diff --git a/ports/geckolib/properties.mako.rs b/ports/geckolib/properties.mako.rs
index 42e127ed791..0257ba9e8d6 100644
--- a/ports/geckolib/properties.mako.rs
+++ b/ports/geckolib/properties.mako.rs
@@ -267,7 +267,7 @@ def set_gecko_property(ffi_name, expr):
 % endif
 </%def>
 
-<%def name="impl_style_coord(ident, unit_ffi_name, union_ffi_name)">
+<%def name="impl_split_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});
@@ -281,6 +281,10 @@ def set_gecko_property(ffi_name, expr):
     }
 </%def>
 
+<%def name="impl_style_coord(ident, gecko_ffi_name)">
+<%call expr="impl_split_style_coord(ident, '%s.mUnit' % gecko_ffi_name, '%s.mValue' % gecko_ffi_name)"></%call>
+</%def>
+
 <%def name="impl_style_struct(style_struct)">
 impl ${style_struct.gecko_struct_name} {
     #[allow(dead_code, unused_variables)]
@@ -354,14 +358,17 @@ impl Debug for ${style_struct.gecko_ffi_name} {
    # These are booleans.
    force_stub += ["page-break-after", "page-break-before"]
 
-   simple_types = ["Number", "Opacity"]
+   # Types used with predefined_type()-defined properties that we can auto-generate.
+   predefined_types = {
+       "LengthOrPercentageOrAuto": impl_style_coord,
+       "Number": impl_simple,
+       "Opacity": impl_simple,
+   }
 
    keyword_longhands = [x for x in longhands if x.keyword and not x.name in force_stub]
-   simple_longhands = [x for x in longhands
-                       if x.predefined_type in simple_types and not x.name in force_stub]
-
-   autogenerated_longhands = keyword_longhands + simple_longhands
-   stub_longhands = [x for x in longhands if x not in autogenerated_longhands]
+   predefined_longhands = [x for x in longhands
+                           if x.predefined_type in predefined_types and not x.name in force_stub]
+   stub_longhands = [x for x in longhands if x not in keyword_longhands + predefined_longhands]
 %>
 impl ${style_struct.trait_name} for ${style_struct.gecko_struct_name} {
     /*
@@ -372,12 +379,13 @@ impl ${style_struct.trait_name} for ${style_struct.gecko_struct_name} {
     /*
      * Auto-Generated Methods.
      */
-    % for longhand in keyword_longhands:
-    <%call expr="impl_keyword(longhand.ident, longhand.gecko_ffi_name, longhand.keyword, longhand.need_clone)"></%call>
-    % endfor
-    % for longhand in simple_longhands:
-    <%call expr="impl_simple(longhand.ident, longhand.gecko_ffi_name)"></%call>
-    % endfor
+    <%
+    for longhand in keyword_longhands:
+        impl_keyword(longhand.ident, longhand.gecko_ffi_name, longhand.keyword, longhand.need_clone)
+    for longhand in predefined_longhands:
+        impl_fn = predefined_types[longhand.predefined_type]
+        impl_fn(longhand.ident, longhand.gecko_ffi_name)
+    %>
 
     /*
      * Stubs.
@@ -461,8 +469,9 @@ fn static_assert() {
                   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) %>
+    <% impl_split_style_coord("margin_%s" % side.ident,
+                              "mMargin.mUnits[%s]" % side.index,
+                              "mMargin.mValues[%s]" % side.index) %>
     % endfor
 </%self:impl_trait>
 
@@ -471,8 +480,9 @@ fn static_assert() {
                   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) %>
+    <% impl_split_style_coord("padding_%s" % side.ident,
+                              "mPadding.mUnits[%s]" % side.index,
+                              "mPadding.mValues[%s]" % side.index) %>
     % endfor
 </%self:impl_trait>
 
@@ -481,8 +491,9 @@ fn static_assert() {
                   skip_longhands="${skip_position_longhands}">
 
     % for side in SIDES:
-    <% impl_style_coord("%s" % side.ident,
-                        "mOffset.mUnits[%s]" % side.index, "mOffset.mValues[%s]" % side.index) %>
+    <% impl_split_style_coord("%s" % side.ident,
+                              "mOffset.mUnits[%s]" % side.index,
+                              "mOffset.mValues[%s]" % side.index) %>
     % endfor
 </%self:impl_trait>