diff --git a/bin/tex2mml b/bin/tex2mml
index 029265bd..bc8f1127 100755
--- a/bin/tex2mml
+++ b/bin/tex2mml
@@ -51,6 +51,10 @@ var argv = require("yargs")
     notexhints: {
       boolean: true,
       describe: "don't add TeX-specific classes"
+    },
+    allowinvalid: {
+      boolean: true,
+      describe: "do not fail for invalid TeX commands (display red)"
     }
   })
   .argv;
@@ -61,7 +65,8 @@ mjAPI.config({
       semantics: argv.semantics,
       texHints: !argv.notexhints
     }
-  }
+  },
+  allowInvalidTeX: argv.allowinvalid
 });
 mjAPI.start();
 
diff --git a/bin/tex2png b/bin/tex2png
index 8770ee20..2e3e3f35 100755
--- a/bin/tex2png
+++ b/bin/tex2png
@@ -52,12 +52,16 @@ var argv = require("yargs")
     width: {
       default: 100,
       describe: "width of container in ex"
+    },
+    allowinvalid: {
+      boolean: true,
+      describe: "do not fail for invalid TeX commands (display red)"
     }
   })
   .argv;
 
 if (argv.font === "STIX") argv.font = "STIX-Web";
-mjAPI.config({MathJax: {SVG: {font: argv.font}}});
+mjAPI.config({MathJax: {SVG: {font: argv.font}}, allowInvalidTeX: argv.allowinvalid});
 mjAPI.start();
 
 mjAPI.typeset({
diff --git a/bin/tex2svg b/bin/tex2svg
index de69e79c..d5c771ec 100755
--- a/bin/tex2svg
+++ b/bin/tex2svg
@@ -59,12 +59,16 @@ var argv = require("yargs")
     width: {
       default: 100,
       describe: "width of container in ex"
+    },
+    allowinvalid: {
+      boolean: true,
+      describe: "do not fail for invalid TeX commands (display red)"
     }
   })
   .argv;
 
 if (argv.font === "STIX") argv.font = "STIX-Web";
-mjAPI.config({MathJax: {SVG: {font: argv.font}}});
+mjAPI.config({MathJax: {SVG: {font: argv.font}}, allowInvalidTeX: argv.allowinvalid});
 mjAPI.start();
 
 mjAPI.typeset({
diff --git a/bin/tex2svg-filter b/bin/tex2svg-filter
index e103475a..a84c8e09 100755
--- a/bin/tex2svg-filter
+++ b/bin/tex2svg-filter
@@ -63,12 +63,16 @@ var argv = require("yargs")
     width: {
       default: 100,
       describe: "width of container in ex"
+    },
+    allowinvalid: {
+      boolean: true,
+      describe: "do not fail for invalid TeX commands (display red)"
     }
   })
   .argv;
 
 if (argv.font === "STIX") argv.font = "STIX-Web";
-mjAPI.config({MathJax: {SVG: {font: argv.font}}});
+mjAPI.config({MathJax: {SVG: {font: argv.font}}, allowInvalidTeX: argv.allowinvalid});
 mjAPI.start();
 
 var prefix = argv._[0];  // the file prefix
diff --git a/lib/mj-single.js b/lib/mj-single.js
index fe8c22d5..f2307039 100644
--- a/lib/mj-single.js
+++ b/lib/mj-single.js
@@ -37,6 +37,7 @@ var speech = require('speech-rule-engine');
 var displayMessages = false;      // don't log Message.Set() calls
 var displayErrors = true;         // show error messages on the console
 var undefinedChar = false;        // unknown characters are not saved in the error array
+var allowInvalidTeX = false;      // invalid TeX commands cause failure
 
 var defaults = {
   ex: 6,                          // ex-size in pixels
@@ -308,6 +309,7 @@ function ConfigureMathJax() {
     }
   };
 
+  if (allowInvalidTeX) { window.MathJax.TeX.extensions.push("noUndefined.js"); }
   if (MathJaxConfig) {Insert(window.MathJax,MathJaxConfig)}
 }
 
@@ -664,5 +666,6 @@ exports.config = function (config) {
   if (config.displayMessages != null)    {displayMessages = config.displayMessages}
   if (config.displayErrors != null)      {displayErrors   = config.displayErrors}
   if (config.undefinedCharError != null) {undefinedChar   = config.undefinedCharError}
+  if (config.allowInvalidTeX != null)    {allowInvalidTeX = config.allowInvalidTeX}
   if (config.MathJax) {MathJaxConfig = config.MathJax}
 }