diff --git a/bin/documentation.js b/bin/documentation.js
index 78ddee0..c0b74a0 100755
--- a/bin/documentation.js
+++ b/bin/documentation.js
@@ -67,6 +67,13 @@ function parseArgs() {
   var command = argv._[0],
     inputs = argv._.slice(1);
 
+  if (!commands[command]) {
+    yargs.showHelp();
+    var suggestion = [argv['$0'], 'build'].concat(process.argv.slice(2)).join(' ');
+    process.stderr.write('Unknown command: ' + command + '.  Did you mean "' + suggestion + '"?\n');
+    process.exit(1);
+  }
+
   if (inputs.length == 0) {
     try {
       var p = require(path.resolve('package.json'));
diff --git a/test/bin.js b/test/bin.js
index c4273df..82b60c4 100644
--- a/test/bin.js
+++ b/test/bin.js
@@ -122,6 +122,14 @@ test('invalid arguments', function (group) {
     });
   }, options);
 
+  group.test('bad command', function (t) {
+    documentation(['-f html fixture/internal.input.js'], function (err, stdout, stderr) {
+      t.ok(err.code, 'exits nonzero');
+      t.ok(stderr.match(/Unknown command/), 'reports unknown command');
+      t.end();
+    });
+  });
+
   group.end();
 });