diff --git a/components/style/values/generics/border.rs b/components/style/values/generics/border.rs
index 33f9cd8b8a6..215c2fd23e5 100644
--- a/components/style/values/generics/border.rs
+++ b/components/style/values/generics/border.rs
@@ -151,13 +151,18 @@ impl<L: Clone> From<L> for BorderCornerRadius<L> {
 }
 
 impl<L> ToCss for BorderCornerRadius<L>
-    where L: ToCss,
+    where L: ToCss + PartialEq,
 {
     fn to_css<W>(&self, dest: &mut W) -> fmt::Result
         where W: fmt::Write
     {
         self.0.width.to_css(dest)?;
-        dest.write_str(" ")?;
-        self.0.height.to_css(dest)
+
+        if self.0.height != self.0.width {
+            dest.write_str(" ")?;
+            self.0.height.to_css(dest)?;
+        }
+
+        Ok(())
     }
 }
diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index a451a31a9c2..7c4260ca22f 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -27301,7 +27301,7 @@
    "testharness"
   ],
   "mozilla/calc.html": [
-   "4f65929cacf623da2d3e310a6663d6165a1b0cdc",
+   "2b6f029f2393830ea8dce5f26a5c9caaae65944f",
    "testharness"
   ],
   "mozilla/canvas.initial.reset.2dstate.html": [
diff --git a/tests/wpt/mozilla/tests/mozilla/calc.html b/tests/wpt/mozilla/tests/mozilla/calc.html
index 6f2a77a1d4f..2408f196c00 100644
--- a/tests/wpt/mozilla/tests/mozilla/calc.html
+++ b/tests/wpt/mozilla/tests/mozilla/calc.html
@@ -146,10 +146,10 @@ var otherProperties = [
   ['perspective-origin', 'calc(1px + 0%)', 'calc(0% + 1px) center'],
   ['background-size', 'calc(1px + 0%)', 'calc(0% + 1px) auto'],
   ['background-position', 'calc(1px + 0%) calc(2px + 0%)', 'calc(0% + 1px) calc(0% + 2px)'],
-  ['border-top-left-radius', 'calc(1px + 0%)', 'calc(0% + 1px) calc(0% + 1px)'],
-  ['border-bottom-left-radius', 'calc(1px + 0%)', 'calc(0% + 1px) calc(0% + 1px)'],
-  ['border-top-right-radius', 'calc(1px + 0%)', 'calc(0% + 1px) calc(0% + 1px)'],
-  ['border-bottom-right-radius', 'calc(1px + 0%)', 'calc(0% + 1px) calc(0% + 1px)'],
+  ['border-top-left-radius', 'calc(1px + 0%)', 'calc(0% + 1px)'],
+  ['border-bottom-left-radius', 'calc(1px + 0%)', 'calc(0% + 1px)'],
+  ['border-top-right-radius', 'calc(1px + 0%)', 'calc(0% + 1px)'],
+  ['border-bottom-right-radius', 'calc(1px + 0%)', 'calc(0% + 1px)'],
   ['counter-increment', 'foo calc(1 + 1)', 'foo calc(2)'],
 ];