diff --git a/unpacked/extensions/toMathML.js b/unpacked/extensions/toMathML.js
index e96c57327..4a0949f61 100644
--- a/unpacked/extensions/toMathML.js
+++ b/unpacked/extensions/toMathML.js
@@ -91,7 +91,7 @@ MathJax.Hub.Register.LoadHook("[MathJax]/jax/element/mml/jax.js",function () {
       if (typeof(value) === "string" &&
           value.replace(/ /g,"").match(/^(([-+])?(\d+(\.\d*)?|\.\d+))mu$/)) {
         // FIXME:  should take scriptlevel into account
-        return RegExp.$2+((1/18)*RegExp.$3).toFixed(3).replace(/\.?0+$/,"")+"em";
+        return (RegExp.$2||"")+((1/18)*RegExp.$3).toFixed(3).replace(/\.?0+$/,"")+"em";
       }
       else if (this.toMathMLvariants[value]) {return this.toMathMLvariants[value]}
       return this.toMathMLquote(value);
diff --git a/unpacked/jax/output/HTML-CSS/autoload/mtable.js b/unpacked/jax/output/HTML-CSS/autoload/mtable.js
index ab2480352..d4f03d1bb 100644
--- a/unpacked/jax/output/HTML-CSS/autoload/mtable.js
+++ b/unpacked/jax/output/HTML-CSS/autoload/mtable.js
@@ -167,7 +167,7 @@ MathJax.Hub.Register.StartupHook("HTML-CSS Jax Ready",function () {
       var Y, fY, n = "";
       if (typeof(values.align) !== "string") {values.align = String(values.align)}
       if (values.align.match(/(top|bottom|center|baseline|axis)( +(-?\d+))?/))
-        {n = RegExp.$3; values.align = RegExp.$1} else {values.align = this.defaults.align}
+        {n = RegExp.$3||""; values.align = RegExp.$1} else {values.align = this.defaults.align}
       if (n !== "") {
         //
         //  Find the height of the given row
diff --git a/unpacked/jax/output/NativeMML/jax.js b/unpacked/jax/output/NativeMML/jax.js
index 7a1212e6b..a693afbf0 100644
--- a/unpacked/jax/output/NativeMML/jax.js
+++ b/unpacked/jax/output/NativeMML/jax.js
@@ -518,7 +518,7 @@
 	value = String(value);
 	if (nMML.NAMEDSPACE[value]) {value = nMML.NAMEDSPACE[value]} // MP doesn't do negative spaces
 	else if (value.match(/^\s*(([-+])?(\d+(\.\d*)?|\.\d+))\s*mu\s*$/))
-          {value = RegExp.$2+((1/18)*RegExp.$3).toFixed(3).replace(/\.?0+$/,"")+"em"} // FIXME:  should take scriptlevel into account
+          {value = (RegExp.$2||"")+((1/18)*RegExp.$3).toFixed(3).replace(/\.?0+$/,"")+"em"} // FIXME:  should take scriptlevel into account
 	else if (this.NativeMMLvariants[value]) {value = this.NativeMMLvariants[value]}
 	return value;
       },