diff --git a/src/client/ClientDataManager.js b/src/client/ClientDataManager.js
index ad7c0285c..62924904e 100644
--- a/src/client/ClientDataManager.js
+++ b/src/client/ClientDataManager.js
@@ -84,7 +84,7 @@ class ClientDataManager {
   }
 
   killUser(user) {
-    this.users.delete(user.id);
+    this.client.users.delete(user.id);
   }
 
   killChannel(channel) {
diff --git a/src/structures/GuildChannel.js b/src/structures/GuildChannel.js
index d5304aa26..e39d1bb89 100644
--- a/src/structures/GuildChannel.js
+++ b/src/structures/GuildChannel.js
@@ -137,7 +137,7 @@ class GuildChannel extends Channel {
       const roleOverwrites = [];
       const memberOverwrites = [];
 
-      for (const overwrite of this.permissionOverwrites) {
+      for (const overwrite of this.permissionOverwrites.values()) {
         if (overwrite.id === member.id) {
           memberOverwrites.push(overwrite);
         } else if (memberRoles.indexOf(overwrite.id) > -1) {
diff --git a/src/structures/interface/TextBasedChannel.js b/src/structures/interface/TextBasedChannel.js
index 7554722aa..cd30fbfe4 100644
--- a/src/structures/interface/TextBasedChannel.js
+++ b/src/structures/interface/TextBasedChannel.js
@@ -166,7 +166,7 @@ class TextBasedChannel {
     }
 
     if (this.messages.size >= maxSize) {
-      this.messages.delete(Array.from(this.messages.keys())[0]);
+      this.messages.delete(this.messages.keys().next().value);
     }
 
     this.messages.set(message.id, message);
diff --git a/src/util/Collection.js b/src/util/Collection.js
index f33053a33..67168cb24 100644
--- a/src/util/Collection.js
+++ b/src/util/Collection.js
@@ -77,6 +77,8 @@ class Collection extends Map {
    * collection.getAll('username', 'Bob');
    */
   findAll(key, value) {
+    if (typeof key !== 'string') throw new TypeError('key must be a string');
+    if (typeof value === 'undefined') throw new Error('value must be specified');
     const results = [];
     for (const item of this.values()) {
       if (item[key] === value) {
@@ -95,6 +97,8 @@ class Collection extends Map {
    * collection.get('id', '123123...');
    */
   find(key, value) {
+    if (typeof key !== 'string') throw new TypeError('key must be a string');
+    if (typeof value === 'undefined') throw new Error('value must be specified');
     for (const item of this.values()) {
       if (item[key] === value) {
         return item;