diff --git a/src/buildHTML.js b/src/buildHTML.js
index b54d6a85..401012ff 100644
--- a/src/buildHTML.js
+++ b/src/buildHTML.js
@@ -571,12 +571,6 @@ export const groupTypes = {
         return makeSpan(["mrel", "x-arrow"], [vlist], options);
     },
 
-    mclass(group, options) {
-        const elements = buildExpression(group.value.value, options, true);
-
-        return makeSpan([group.value.mclass], elements, options);
-    },
-
     raisebox(group, options) {
         const body = groupTypes.sizing({value: {
             value: [{
diff --git a/src/buildMathML.js b/src/buildMathML.js
index a828e4f7..aecbbea0 100644
--- a/src/buildMathML.js
+++ b/src/buildMathML.js
@@ -275,11 +275,6 @@ groupTypes.xArrow = function(group, options) {
     return node;
 };
 
-groupTypes.mclass = function(group, options) {
-    const inner = buildExpression(group.value.value, options);
-    return new mathMLTree.MathNode("mstyle", inner);
-};
-
 groupTypes.raisebox = function(group, options) {
     const node = new mathMLTree.MathNode(
         "mpadded", [buildGroup(group.value.body, options)]);
diff --git a/src/functions.js b/src/functions.js
index f9c7c808..4360025a 100644
--- a/src/functions.js
+++ b/src/functions.js
@@ -1,7 +1,6 @@
 // @flow
 /** Include this to ensure that all functions are defined. */
 import ParseError from "./ParseError";
-import ParseNode from "./ParseNode";
 import {
     default as _defineFunction,
     ordargument,
@@ -51,70 +50,7 @@ import "./functions/kern";
 
 import "./functions/phantom";
 
-// Math class commands except \mathop
-defineFunction("mclass", [
-    "\\mathord", "\\mathbin", "\\mathrel", "\\mathopen",
-    "\\mathclose", "\\mathpunct", "\\mathinner",
-], {
-    numArgs: 1,
-}, function(context, args) {
-    const body = args[0];
-    return {
-        type: "mclass",
-        mclass: "m" + context.funcName.substr(5),
-        value: ordargument(body),
-    };
-});
-
-// Build a relation or stacked op by placing one symbol on top of another
-defineFunction("mclass", ["\\stackrel", "\\overset", "\\underset"], {
-    numArgs: 2,
-}, function(context, args) {
-    const baseArg = args[1];
-    const shiftedArg = args[0];
-
-    let mclass = "mrel";  // default. May change below.
-    if (context.funcName !== "\\stackrel") {
-        // LaTeX applies \binrel spacing to \overset and \underset.
-        // \binrel spacing varies with (bin|rel|ord) of the atom in the argument.
-        // We'll do the same.
-        let atomType = "";
-        if (baseArg.type === "ordgroup") {
-            atomType = baseArg.value[0].type;
-        } else {
-            atomType = baseArg.type;
-        }
-        if (/^(bin|rel)$/.test(atomType)) {
-            mclass = "m" + atomType;
-        } else {
-            // This may capture some instances in which the baseArg is more than
-            // just a single symbol. Say a \overset inside an \overset.
-            // TODO: A more comprehensive way to determine the baseArg type.
-            mclass = "mord";
-        }
-    }
-
-    const baseOp = new ParseNode("op", {
-        type: "op",
-        limits: true,
-        alwaysHandleSupSub: true,
-        symbol: false,
-        suppressBaseShift: context.funcName !== "\\stackrel",
-        value: ordargument(baseArg),
-    }, baseArg.mode);
-
-    const supsub = new ParseNode("supsub", {
-        base: baseOp,
-        sup: context.funcName === "\\underset" ? null : shiftedArg,
-        sub: context.funcName === "\\underset" ? shiftedArg : null,
-    }, shiftedArg.mode);
-
-    return {
-        type: "mclass",
-        mclass: mclass,
-        value: [supsub],
-    };
-});
+import "./functions/mclass";
 
 import "./functions/mod";
 
diff --git a/src/functions/mclass.js b/src/functions/mclass.js
new file mode 100644
index 00000000..3b5eb23d
--- /dev/null
+++ b/src/functions/mclass.js
@@ -0,0 +1,100 @@
+// @flow
+import defineFunction, {ordargument} from "../defineFunction";
+import buildCommon from "../buildCommon";
+import mathMLTree from "../mathMLTree";
+import ParseNode from "../ParseNode";
+
+import * as html from "../buildHTML";
+import * as mml from "../buildMathML";
+
+const makeSpan = buildCommon.makeSpan;
+
+function htmlBuilder(group, options) {
+    const elements = html.buildExpression(group.value.value, options, true);
+    return makeSpan([group.value.mclass], elements, options);
+}
+
+function mathmlBuilder(group, options) {
+    const inner = mml.buildExpression(group.value.value, options);
+    return new mathMLTree.MathNode("mstyle", inner);
+}
+
+// Math class commands except \mathop
+defineFunction({
+    type: "mclass",
+    names: [
+        "\\mathord", "\\mathbin", "\\mathrel", "\\mathopen",
+        "\\mathclose", "\\mathpunct", "\\mathinner",
+    ],
+    props: {
+        numArgs: 1,
+    },
+    handler(context, args) {
+        const body = args[0];
+        return {
+            type: "mclass",
+            mclass: "m" + context.funcName.substr(5),
+            value: ordargument(body),
+        };
+    },
+    htmlBuilder,
+    mathmlBuilder,
+});
+
+// Build a relation or stacked op by placing one symbol on top of another
+defineFunction({
+    type: "mclass",
+    names: ["\\stackrel", "\\overset", "\\underset"],
+    props: {
+        numArgs: 2,
+    },
+    handler(context, args) {
+        const baseArg = args[1];
+        const shiftedArg = args[0];
+
+        let mclass = "mrel";  // default. May change below.
+        if (context.funcName !== "\\stackrel") {
+            // LaTeX applies \binrel spacing to \overset and \underset. \binrel
+            // spacing varies with (bin|rel|ord) of the atom in the argument.
+            // We'll do the same.
+            let atomType = "";
+            if (baseArg.type === "ordgroup") {
+                atomType = baseArg.value[0].type;
+            } else {
+                atomType = baseArg.type;
+            }
+            if (/^(bin|rel)$/.test(atomType)) {
+                mclass = "m" + atomType;
+            } else {
+                // This may capture some instances in which the baseArg is more
+                // than just a single symbol. Say a \overset inside an \overset.
+                // TODO: A more comprehensive way to determine the baseArg type.
+                mclass = "mord";
+            }
+        }
+
+        const baseOp = new ParseNode("op", {
+            type: "op",
+            limits: true,
+            alwaysHandleSupSub: true,
+            symbol: false,
+            suppressBaseShift: context.funcName !== "\\stackrel",
+            value: ordargument(baseArg),
+        }, baseArg.mode);
+
+        const supsub = new ParseNode("supsub", {
+            base: baseOp,
+            sup: context.funcName === "\\underset" ? null : shiftedArg,
+            sub: context.funcName === "\\underset" ? shiftedArg : null,
+        }, shiftedArg.mode);
+
+        return {
+            type: "mclass",
+            mclass: mclass,
+            value: [supsub],
+        };
+    },
+    htmlBuilder,
+    mathmlBuilder,
+});
+