diff --git a/index.js b/index.js
index 1150335..750c2bf 100644
--- a/index.js
+++ b/index.js
@@ -65,6 +65,10 @@ function pathToRegexp(path, keys, options) {
     return new RegExp(path.join('|'), flags);
   }
 
+  if (typeof path !== 'string') {
+    throw new TypeError('path must be a string, array of strings, or regular expression');
+  }
+
   path = path.replace(
     /\\.|(\/)?(\.)?:(\w+)(\(.*?\))?(\*)?(\?)?|[.*]|\/\(/g,
     function (match, slash, format, key, capture, star, optional, offset) {
diff --git a/test.js b/test.js
index 63ecb86..d239195 100644
--- a/test.js
+++ b/test.js
@@ -2,6 +2,12 @@ var pathToRegExp = require('./');
 var assert = require('assert');
 
 describe('path-to-regexp', function () {
+  it('should throw on invalid input', function () {
+    assert.throws(function () {
+      pathToRegExp(function () {});
+    }, /path must be a string, array of strings, or regular expression/);
+  });
+
   describe('strings', function () {
     it('should match simple paths', function () {
       var params = [];