diff --git a/layout/reftests/mathml/semantics-1-ref.xhtml b/layout/reftests/mathml/semantics-1-ref.xhtml
index f00abdad91d9..567173b434ee 100644
--- a/layout/reftests/mathml/semantics-1-ref.xhtml
+++ b/layout/reftests/mathml/semantics-1-ref.xhtml
@@ -23,7 +23,7 @@
 <!-- embellished operator (bug 21479) -->
 <p><math xmlns="http://www.w3.org/1998/Math/MathML">
   <mover>
-    <mtext>■□■□■□■□■□■□</mtext>
+    <mspace width="300px" height="10px" mathbackground="black"></mspace>
     <mo>&#xaf;</mo>
   </mover>
 </math></p>
diff --git a/layout/reftests/mathml/semantics-1.xhtml b/layout/reftests/mathml/semantics-1.xhtml
index 39625261194d..52dc05b89c4b 100644
--- a/layout/reftests/mathml/semantics-1.xhtml
+++ b/layout/reftests/mathml/semantics-1.xhtml
@@ -21,7 +21,7 @@
 <!-- embellished operator (bug 21479) -->
 <p><math xmlns="http://www.w3.org/1998/Math/MathML">
   <mover>
-    <mtext>■□■□■□■□■□■□</mtext>
+    <mspace width="300px" height="10px" mathbackground="black"></mspace>
     <semantics><mo>&#xaf;</mo></semantics>
   </mover>
 </math></p>