diff --git a/core/modules/commands/makelibrary.js b/core/modules/commands/makelibrary.js
index c2e15ef37..1e0035dab 100644
--- a/core/modules/commands/makelibrary.js
+++ b/core/modules/commands/makelibrary.js
@@ -33,7 +33,7 @@ Command.prototype.execute = function() {
 		tiddlers = {};
 	// Collect up the library plugins
 	var collectPlugins = function(folder) {
-			var pluginFolders = fs.readdirSync(folder);
+			var pluginFolders = $tw.utils.getSubdirectories(folder);
 			for(var p=0; p<pluginFolders.length; p++) {
 				if(!$tw.boot.excludeRegExp.test(pluginFolders[p])) {
 					pluginFields = $tw.loadPluginFolder(path.resolve(folder,"./" + pluginFolders[p]));
@@ -44,7 +44,7 @@ Command.prototype.execute = function() {
 			}
 		},
 		collectPublisherPlugins = function(folder) {
-			var publisherFolders = fs.readdirSync(folder);
+			var publisherFolders = $tw.utils.getSubdirectories(folder);
 			for(var t=0; t<publisherFolders.length; t++) {
 				if(!$tw.boot.excludeRegExp.test(publisherFolders[t])) {
 					collectPlugins(path.resolve(folder,"./" + publisherFolders[t]));
diff --git a/core/modules/utils/filesystem.js b/core/modules/utils/filesystem.js
index 999239450..43d6039d5 100644
--- a/core/modules/utils/filesystem.js
+++ b/core/modules/utils/filesystem.js
@@ -15,6 +15,22 @@ File system utilities
 var fs = require("fs"),
 	path = require("path");
 
+/*
+Return the subdirectories of a path
+*/
+exports.getSubdirectories = function(dirPath) {
+	if(!$tw.utils.isDirectory(dirPath)) {
+		return null;
+	}
+	var subdirs = [];
+	$tw.utils.each(fs.readdirSync(dirPath),function(itemPath) {
+		if($tw.utils.isDirectory(itemPath)) {
+			subdirs.push(itemPath);
+		}
+	});
+	return subdirs;
+}
+
 /*
 Recursively (and synchronously) copy a directory and all its content
 */