diff --git a/src/util/Collection.js b/src/util/Collection.js
index f33053a3..67168cb2 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;