diff --git a/css-text-decor-4/Overview.bs b/css-text-decor-4/Overview.bs
index 05aec3c1c18..9065e6856ea 100644
--- a/css-text-decor-4/Overview.bs
+++ b/css-text-decor-4/Overview.bs
@@ -339,7 +339,8 @@ Text Decoration Line Thickness: the 'text-decoration-thickness' property</h3>
 		<dt><dfn><<length>></dfn>
 		<dd>
 			Specifies the thickness of text decoration lines as a fixed length.
-			The UA should round to the nearest positive integer.
+			The UA should round the actual value to the nearest integer device pixel,
+			and ensure it is at least one device pixel.
 
 			Note: A length will inherit as a fixed value,
 			and will not scale with the font.
@@ -347,7 +348,8 @@ Text Decoration Line Thickness: the 'text-decoration-thickness' property</h3>
 		<dt><dfn><<percentage>></dfn>
 		<dd>
 			<p>Specifies the thickness of text decoration lines as a percentage of ''1em''.
-			The UA should round to the nearest positive integer.
+			The UA should round the actual value to the nearest integer device pixel,
+			and ensure it is at least one device pixel.
 
 			Note: A percentage will inherit as a relative value,
 			and will therefore scale with changes in the font as it inherits.