diff --git a/src/librustdoc/html/static/rustdoc.css b/src/librustdoc/html/static/rustdoc.css
index 8887bca3c5962..d091cc0c0965b 100644
--- a/src/librustdoc/html/static/rustdoc.css
+++ b/src/librustdoc/html/static/rustdoc.css
@@ -1082,8 +1082,8 @@ h3 > .collapse-toggle, h4 > .collapse-toggle {
 
 pre.rust {
 	position: relative;
-	tab-width: 4;
-	-moz-tab-width: 4;
+	tab-size: 4;
+	-moz-tab-size: 4;
 }
 
 .search-failed {