--- a/dom/animation/test/mozilla/test_distance_of_transform.html
+++ b/dom/animation/test/mozilla/test_distance_of_transform.html
@@ -187,35 +187,35 @@ test(function(t) {
   assert_equals(dist, Math.sqrt(2 * 2 + 0.5 * 0.5), 'distance of skew');
 }, 'Test distance of skew functions');
 
 test(function(t) {
   var target = addDiv(t);
   var dist = getDistance(target, 'transform',
                          'perspective(128px)',
                          'none');
-  assert_equals(dist, 1/128, 'distance of perspective');
+  assert_equals(dist, 128, 'distance of perspective');
 }, 'Test distance of perspective function and none');
 
 test(function(t) {
   var target = addDiv(t);
   // perspective(0) is treated as perspective(inf) because perspective length
   // should be greater than or equal to zero.
   var dist = getDistance(target, 'transform',
                          'perspective(128px)',
                          'perspective(0)');
-  assert_equals(dist, 1/128, 'distance of perspective');
+  assert_equals(dist, 128, 'distance of perspective');
 }, 'Test distance of perspective function and an invalid perspective');
 
 test(function(t) {
   var target = addDiv(t);
   var dist = getDistance(target, 'transform',
                          'perspective(128px)',
                          'perspective(1024px)');
-  assert_equals(dist, 1/128 - 1/1024, 'distance of perspective');
+  assert_equals(dist, 1024 - 128, 'distance of perspective');
 }, 'Test distance of perspective functions');
 
 test(function(t) {
   var target = addDiv(t);
   var sin_30 = Math.sin(Math.PI / 6);
   var cos_30 = Math.cos(Math.PI / 6);
   // matrix => translate(100, 0) rotate(30deg).
   var matrix = createMatrixFromArray([ cos_30, sin_30,

--- a/servo/components/style/properties/helpers/animated_properties.mako.rs
+++ b/servo/components/style/properties/helpers/animated_properties.mako.rs
@@ -2627,26 +2627,17 @@ impl ComputeSquaredDistance for Computed
                 &TransformOperation::Rotate(ta),
             ) => {
                 fa.compute_squared_distance(&ta)
             }
             (
                 &TransformOperation::Perspective(ref fd),
                 &TransformOperation::Perspective(ref td),
             ) => {
-                let mut fd_matrix = Matrix3D::identity();
-                let mut td_matrix = Matrix3D::identity();
-                if fd.px() > 0. {
-                    fd_matrix.m34 = -1. / fd.px();
-                }
-
-                if td.px() > 0. {
-                    td_matrix.m34 = -1. / td.px();
-                }
-                fd_matrix.compute_squared_distance(&td_matrix)
+                fd.compute_squared_distance(td)
             }
             (
                 &TransformOperation::Perspective(ref p),
                 &TransformOperation::Matrix3D(ref m),
             ) | (
                 &TransformOperation::Matrix3D(ref m),
                 &TransformOperation::Perspective(ref p),
             ) => {