--- a/servo/components/style/properties/helpers/animated_properties.mako.rs
+++ b/servo/components/style/properties/helpers/animated_properties.mako.rs
@@ -2106,16 +2106,18 @@ fn cross(row1: [f32; 3], row2: [f32; 3])
     [
         row1[1] * row2[2] - row1[2] * row2[1],
         row1[2] * row2[0] - row1[0] * row2[2],
         row1[0] * row2[1] - row1[1] * row2[0]
     ]
 }
 
 impl Animate for Scale3D {
+    // FIXME(emilio): why does this do something different than ComputedScale
+    // for addition?
     fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
         Ok(Scale3D(
             animate_multiplicative_factor(self.0, other.0, procedure)?,
             animate_multiplicative_factor(self.1, other.1, procedure)?,
             animate_multiplicative_factor(self.2, other.2, procedure)?,
         ))
     }
 }