diff --git a/index.js b/index.js
index 9b6195d..0d21473 100644
--- a/index.js
+++ b/index.js
@@ -37,6 +37,22 @@ function normalizeManifestPaths (tokensByFile, rootDir) {
 }
 
 var cssExt = /\.css$/;
+
+// caches
+//
+// persist these for as long as the process is running. #32
+
+// keep track of css files visited
+var filenames = [];
+
+// keep track of all tokens so we can avoid duplicates
+var tokensByFile = {};
+
+// keep track of all source files for later builds: when
+// using watchify, not all files will be caught on subsequent
+// bundles
+var sourceByFile = {};
+
 module.exports = function (browserify, options) {
   options = options || {};
 
@@ -91,17 +107,6 @@ module.exports = function (browserify, options) {
     return plugin;
   });
 
-  // keep track of css files visited
-  var filenames = [];
-
-  // keep track of all tokens so we can avoid duplicates
-  var tokensByFile = {};
-
-  // keep track of all source files for later builds: when
-  // using watchify, not all files will be caught on subsequent
-  // bundles
-  var sourceByFile = {};
-
   function transform (filename) {
     // only handle .css files
     if (!cssExt.test(filename)) {
diff --git a/package.json b/package.json
index 0e57907..f5536ff 100644
--- a/package.json
+++ b/package.json
@@ -12,6 +12,7 @@
   "devDependencies": {
     "browserify": "^11.0.1",
     "proxyquire": "^1.6.0",
+    "rebundler": "^0.2.0",
     "tape": "^4.0.1"
   },
   "scripts": {
diff --git a/tests/cache.js b/tests/cache.js
new file mode 100644
index 0000000..45c3c59
--- /dev/null
+++ b/tests/cache.js
@@ -0,0 +1,49 @@
+var tape = require('tape');
+
+var browserify = require('browserify');
+var proxyquire = require('proxyquire');
+var fs = require('fs');
+var path = require('path');
+var rebundler = require('rebundler');
+
+var casesDir = path.join(__dirname, 'cases');
+var simpleCaseDir = path.join(casesDir, 'simple');
+var cssOutFilename = 'out.css';
+
+tape('multiple builds', function (t) {
+  var fakeFs = {
+    writeFile: function (filename, content, cb) {
+      var expected = fs.readFileSync(path.join(simpleCaseDir, 'expected.css'), 'utf8');
+
+      t.equal(filename, cssOutFilename, 'correct output filename');
+      t.equal(content, expected, 'output matches expected');
+      cb();
+    }
+  };
+
+  var cssModulesify = proxyquire('../', {
+    fs: fakeFs
+  });
+
+  var getBundler = rebundler(function (cache, packageCache) {
+    return browserify(path.join(simpleCaseDir, 'main.js'), {
+      cache: cache
+    , packageCache: packageCache
+    , fullPaths: true
+    })
+      .plugin(cssModulesify, {
+        rootDir: path.join(simpleCaseDir)
+        , output: cssOutFilename
+      });
+  });
+
+  getBundler().bundle(function (err) {
+    t.error(err, 'initial bundle without a cache does not error');
+
+    getBundler().bundle(function (err2) {
+      t.error(err2, 'second pass bundle with a cache does not error');
+
+      t.end();
+    });
+  });
+});