diff --git a/src/privileges/categories.js b/src/privileges/categories.js
index 11b4767b30..b0f89a9fad 100644
--- a/src/privileges/categories.js
+++ b/src/privileges/categories.js
@@ -68,6 +68,14 @@ module.exports = function(privileges) {
 	};
 
 	privileges.categories.filter = function(privilege, cids, uid, callback) {
+		if (!cids.length) {
+			return callback(null, []);
+		}
+
+		cids = cids.filter(function(cid, index, array) {
+			return array.indexOf(cid) === index;
+		});
+
 		async.parallel({
 			allowedTo: function(next) {
 				helpers.allowedTo(privilege, uid, cids, next);
diff --git a/src/privileges/posts.js b/src/privileges/posts.js
index 71df14ae36..f68a235866 100644
--- a/src/privileges/posts.js
+++ b/src/privileges/posts.js
@@ -77,6 +77,9 @@ module.exports = function(privileges) {
 	};
 
 	privileges.posts.filter = function(privilege, pids, uid, callback) {
+		if (!pids.length) {
+			return callback(null, []);
+		}
 		posts.getCidsByPids(pids, function(err, cids) {
 			if (err) {
 				return callback(err);
diff --git a/src/privileges/topics.js b/src/privileges/topics.js
index 900aa0782d..6a2d321d97 100644
--- a/src/privileges/topics.js
+++ b/src/privileges/topics.js
@@ -76,6 +76,10 @@ module.exports = function(privileges) {
 	};
 
 	privileges.topics.filter = function(privilege, tids, uid, callback) {
+		if (!tids.length) {
+			return callback(null, []);
+		}
+
 		var keys = tids.map(function(tid) {
 			return 'topic:' + tid;
 		});