diff --git a/index.js b/index.js
index 053e5e0..5bcbc91 100644
--- a/index.js
+++ b/index.js
@@ -74,22 +74,30 @@ function normalizeManifestPaths (tokensByFile, rootDir) {
   return output;
 }
 
+function dedupeSources (sources) {
+  var foundHashes = {}
+  Object.keys(sources).forEach(function (key) {
+    var hash = stringHash(sources[key]);
+    if (foundHashes[hash]) {
+      delete sources[key];
+    }
+    else {
+      foundHashes[hash] = true;
+    }
+  })
+}
+
 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 = {};
+// we need a separate loader for each entry point
+var loadersByFile = {};
 
 module.exports = function (browserify, options) {
   options = options || {};
@@ -103,9 +111,10 @@ module.exports = function (browserify, options) {
   var jsonOutFilename = options.json || options.jsonOutput;
   var sourceKey = cssOutFilename;
 
-  // keying our source caches by the name of our output file means we can
-  // isolate css compilation of seperate bundles that are running in parallel
-  sourceByFile[sourceKey] = sourceByFile[sourceKey] || {};
+  var loader = loadersByFile[sourceKey];
+  if (!loader) {
+      loader = loadersByFile[sourceKey] = new FileSystemLoader(rootDir, plugins);
+  }
 
   // PostCSS plugins passed to FileSystemLoader
   var plugins = options.use || options.u;
@@ -158,10 +167,6 @@ module.exports = function (browserify, options) {
       return through();
     }
 
-    // collect visited filenames
-    filenames.push(filename);
-
-    var loader = new FileSystemLoader(rootDir, plugins);
     return through(function noop () {}, function end () {
       var self = this;
 
@@ -170,11 +175,6 @@ module.exports = function (browserify, options) {
 
         assign(tokensByFile, loader.tokensByFile);
 
-        // store this file's source to be written out to disk later
-        sourceByFile[sourceKey][filename] = loader.finalSource;
-
-        compiledCssStream.push(loader.finalSource);
-
         self.queue(output);
         self.queue(null);
       }, function (err) {
@@ -195,19 +195,19 @@ module.exports = function (browserify, options) {
     bundle.emit('css stream', compiledCssStream);
 
     bundle.on('end', function () {
+      // under certain conditions (eg. with shared libraries) we can end up with
+      // multiple occurrences of the same rule, so we need to remove duplicates
+      dedupeSources(loader.sources)
+
       // Combine the collected sources for a single bundle into a single CSS file
-      var files = Object.keys(sourceByFile[sourceKey]);
-      var css;
+      var css = loader.finalSource;
 
       // end the output stream
+      compiledCssStream.push(css);
       compiledCssStream.push(null);
 
       // write the css file
       if (cssOutFilename) {
-        css = files.map(function (file) {
-          return sourceByFile[sourceKey][file];
-        }).join('\n');
-
         fs.writeFile(cssOutFilename, css, function (err) {
           if (err) {
             browserify.emit('error', err);
diff --git a/tests/cases/compose-from-shared/expected.css b/tests/cases/compose-from-shared/expected.css
new file mode 100644
index 0000000..9c004b1
--- /dev/null
+++ b/tests/cases/compose-from-shared/expected.css
@@ -0,0 +1,9 @@
+._shared__shared {
+  background: #000;
+}
+._styles_1__foo {
+  color: #F00;
+}
+._styles_2__bar {
+  background: #BAA;
+}
diff --git a/tests/cases/compose-from-shared/main.js b/tests/cases/compose-from-shared/main.js
new file mode 100644
index 0000000..14cc992
--- /dev/null
+++ b/tests/cases/compose-from-shared/main.js
@@ -0,0 +1,2 @@
+require('./styles-1.css');
+require('./styles-2.css');
diff --git a/tests/cases/compose-from-shared/shared.css b/tests/cases/compose-from-shared/shared.css
new file mode 100644
index 0000000..d6fc168
--- /dev/null
+++ b/tests/cases/compose-from-shared/shared.css
@@ -0,0 +1,3 @@
+.shared {
+  background: #000;
+}
diff --git a/tests/cases/compose-from-shared/styles-1.css b/tests/cases/compose-from-shared/styles-1.css
new file mode 100644
index 0000000..2ffd802
--- /dev/null
+++ b/tests/cases/compose-from-shared/styles-1.css
@@ -0,0 +1,4 @@
+.foo {
+  composes: shared from "./shared.css";
+  color: #F00;
+}
diff --git a/tests/cases/compose-from-shared/styles-2.css b/tests/cases/compose-from-shared/styles-2.css
new file mode 100644
index 0000000..f9d32d8
--- /dev/null
+++ b/tests/cases/compose-from-shared/styles-2.css
@@ -0,0 +1,4 @@
+.bar {
+  composes: shared from "./shared.css";
+  background: #BAA;
+}