diff --git a/unpacked/extensions/TeX/AMSmath.js b/unpacked/extensions/TeX/AMSmath.js
index cf2db4112..f4e373b49 100644
--- a/unpacked/extensions/TeX/AMSmath.js
+++ b/unpacked/extensions/TeX/AMSmath.js
@@ -266,7 +266,7 @@ MathJax.Hub.Register.StartupHook("TeX Jax Ready",function () {
       var den = this.ParseArg(name);
       var frac = MML.mfrac(num,den);
       if (thick !== "") {frac.linethickness = thick}
-      if (left || right) {frac = TEX.fenced(left,frac,right)}
+      if (left || right) {frac = TEX.fixedFence(left,frac.With({texWithDelims:true}),right)}
       if (style !== "") {
         var STYLE = (["D","T","S","SS"])[style];
         if (STYLE == null)
diff --git a/unpacked/jax/input/TeX/jax.js b/unpacked/jax/input/TeX/jax.js
index 9ed03e83b..ac2f9e89d 100644
--- a/unpacked/jax/input/TeX/jax.js
+++ b/unpacked/jax/input/TeX/jax.js
@@ -186,7 +186,7 @@
         if (this.open || this.close) {
           mml.texClass = MML.TEXCLASS.INNER;
           mml.texWithDelims = true;
-          mml = TEX.fenced(this.open,mml,this.close);
+          mml = TEX.fixedFence(this.open,mml,this.close);
         }
         return [STACKITEM.mml(mml), item];
       }
@@ -2146,6 +2146,20 @@
       if (close) {mrow.Append(MML.mo(close).With({fence:true, stretchy:true, texClass:MML.TEXCLASS.CLOSE}))}
       return mrow;
     },
+    /*
+     *  Create an mrow that has \mathchoice using \bigg and \big for the delimiters
+     */
+    fixedFence: function (open,mml,close) {
+      var mrow = MML.mrow().With({open:open, close:close, texClass:MML.TEXCLASS.INNER});
+      if (open) {mrow.Append(this.mathPalette(open,"l"))}
+      if (mml.type === "mrow") {mrow.Append.apply(mrow,mml.data)} else {mrow.Append(mml)}
+      if (close) {mrow.Append(this.mathPalette(close,"r"))}
+      return mrow;
+    },
+    mathPalette: function (fence,side) {
+      var D = '{\\bigg'+side+' '+fence+'}', T = '{\\big'+side+' '+fence+'}';
+      return TEX.Parse('\\mathchoice'+D+T+T+T).mml();
+    },
     
     //
     //  Combine adjacent <mo> elements that are relations