diff --git a/unpacked/jax/output/HTML-CSS/jax.js b/unpacked/jax/output/HTML-CSS/jax.js
index d4e4c33ba..1a99295d4 100644
--- a/unpacked/jax/output/HTML-CSS/jax.js
+++ b/unpacked/jax/output/HTML-CSS/jax.js
@@ -1159,7 +1159,7 @@
       if (this.msieFrameSizeBug) {if (w < T) {w = T}; if (h+d < T) {h = T-d}}
       if (this.msieBorderWidthBug) {T = 0}
       var H = this.Em(h+d-T), D = this.Em(-d-t), W = this.Em(w-T);
-      var B = this.Em(t)+" "+style;
+      var B = this.Px(t)+" "+style;
       var frame = this.addElement(span,"span",{
         style: {border: B, display:"inline-block", overflow:"hidden", width:W, height:H},
         bbox: {h:h, d:d, w:w, rw:w, lw:0, exactW:true}, noAdjust: true, HH:h+d, isMathJax:true