diff --git a/doc/math.css b/doc/math.css
index b09c2258b3..b398c47a95 100644
--- a/doc/math.css
+++ b/doc/math.css
@@ -127,7 +127,7 @@ Names at http://www.w3.org/TR/2002/WD-css3-color-20020219/ 4.3. X11 color keywor
 Quickbook Usage: [role red Some red text]
 
 */
-span.red { inline-block; color: red; }
+span.red { display:inline-block; color: red; }
 span.green { color: green; }
 span.lime { color: #00FF00; }
 span.blue { color: blue; }