diff --git a/katex.js b/katex.js
index 28a2298d..232d9dd1 100644
--- a/katex.js
+++ b/katex.js
@@ -18,6 +18,8 @@ import utils from "./src/utils";
 import type {SettingsOptions} from "./src/Settings";
 import type ParseNode from "./src/ParseNode";
 
+import { defineSymbol } from './src/symbols';
+
 /**
  * Parse and build an expression, and place that expression in the DOM node
  * given.
@@ -68,7 +70,6 @@ const generateParseTree = function(
     return parseTree(expression, settings);
 };
 
-
 /**
  * Generates and returns the katex build tree. This is used for advanced
  * use cases (like rendering to custom output).
@@ -137,4 +138,8 @@ export default {
      * to change. Use at your own risk.
      */
     __renderToHTMLTree: renderToHTMLTree,
+    /**
+     * adds a new symbol to internal symbols table
+    */
+    __defineSymbol: defineSymbol,
 };
diff --git a/package.json b/package.json
index b858360c..4382b25c 100644
--- a/package.json
+++ b/package.json
@@ -61,6 +61,7 @@
     "test:lint": "eslint katex.js katex.webpack.js cli.js webpack.common.js webpack.config.js webpack.dev.js src static test contrib dockers && stylelint src/katex.less",
     "test:flow": "flow",
     "test:jest": "jest",
+    "test:jest:watch": "jest --watch",
     "test:jest:update": "jest --updateSnapshot",
     "test:jest:coverage": "jest --coverage",
     "test:screenshots": "npm run test:screenshots:update -- --verify",
diff --git a/src/symbols.js b/src/symbols.js
index 8c33b60a..58a2035a 100644
--- a/src/symbols.js
+++ b/src/symbols.js
@@ -19,7 +19,7 @@
 
 import type {Mode} from "./types";
 
-type Font = "main" | "ams";
+type Font = "main" | "ams"
 type Group =
     "accent" | "bin" | "close" | "inner" | "mathord" | "op" | "open" | "punct" |
     "rel" | "spacing" | "textord";
@@ -32,7 +32,7 @@ const symbols: {[Mode]: CharInfoMap} = {
 export default symbols;
 
 /** `acceptUnicodeChar = true` is only applicable if `replace` is set. */
-function defineSymbol(
+export function defineSymbol(
     mode: Mode,
     font: Font,
     group: Group,