diff --git a/components/style/values/computed/mod.rs b/components/style/values/computed/mod.rs
index b16dc19529c..1fbaa17c87f 100644
--- a/components/style/values/computed/mod.rs
+++ b/components/style/values/computed/mod.rs
@@ -9,6 +9,7 @@ use context::QuirksMode;
 use euclid::size::Size2D;
 use font_metrics::FontMetricsProvider;
 use media_queries::Device;
+use num_traits::Zero;
 #[cfg(feature = "gecko")]
 use properties;
 use properties::{ComputedValues, StyleBuilder};
@@ -494,8 +495,10 @@ impl ToCss for Shadow {
         dest.write_str(" ")?;
         self.blur_radius.to_css(dest)?;
         dest.write_str(" ")?;
-        self.spread_radius.to_css(dest)?;
-        dest.write_str(" ")?;
+        if self.spread_radius != Au::zero() {
+            self.spread_radius.to_css(dest)?;
+            dest.write_str(" ")?;
+        }
         self.color.to_css(dest)?;
         Ok(())
     }
diff --git a/components/style/values/specified/mod.rs b/components/style/values/specified/mod.rs
index ca86d8d2664..d7046451336 100644
--- a/components/style/values/specified/mod.rs
+++ b/components/style/values/specified/mod.rs
@@ -888,9 +888,10 @@ impl ToCss for Shadow {
         self.offset_y.to_css(dest)?;
         dest.write_str(" ")?;
         self.blur_radius.to_css(dest)?;
-        dest.write_str(" ")?;
-        self.spread_radius.to_css(dest)?;
-
+        if self.spread_radius != Length::zero() {
+            dest.write_str(" ")?;
+            self.spread_radius.to_css(dest)?;
+        }
         if let Some(ref color) = self.color {
             dest.write_str(" ")?;
             color.to_css(dest)?;