diff --git a/src/gateway/Cache.ts b/src/gateway/Cache.ts
index a039afb5..4c659810 100644
--- a/src/gateway/Cache.ts
+++ b/src/gateway/Cache.ts
@@ -4,7 +4,7 @@ export default class Cache {
   store: Store;
 
   constructor(store: Store = {}) {
-    this.store = store;
+    this.store = Object.freeze(store);
   }
 
   get(key: string) {
@@ -19,15 +19,17 @@ export default class Cache {
   }
 
   set(key: string, val: unknown, exp = 86400000, now = new Date().getTime()) {
-    this.store[key] = {
-      val,
-      exp: exp + now,
-    };
-    this.expire();
+    return new Cache({
+      ...this.store,
+      [key]: {
+        val,
+        exp: exp + now,
+      },
+    }).expire();
   }
 
   private expire() {
-    this.store = this.expireMany(this.store, 20);
+    return new Cache(this.expireMany(this.store, 20));
   }
 
   private expired(store: Store, key: string, now = new Date().getTime()) {
diff --git a/src/gateway/HttpGateway.ts b/src/gateway/HttpGateway.ts
index 4fd98f24..cb4e2e2c 100644
--- a/src/gateway/HttpGateway.ts
+++ b/src/gateway/HttpGateway.ts
@@ -13,7 +13,7 @@ export default class HttpGateway {
     }
 
     const result = await axios.get(url, config);
-    this.cache.set(url, result);
+    this.cache = this.cache.set(url, result);
 
     return result;
   }
diff --git a/src/gateway/test/Cache.spec.ts b/src/gateway/test/Cache.spec.ts
index ba65faf5..f793628b 100644
--- a/src/gateway/test/Cache.spec.ts
+++ b/src/gateway/test/Cache.spec.ts
@@ -2,26 +2,19 @@ import Cache from '../Cache';
 
 describe('Cache', () => {
   it('can set and get a value', () => {
-    const cache = new Cache();
-    cache.set('foo', 'baz');
-    expect(cache.get('foo')).toBe('baz');
+    expect(new Cache().set('foo', 'baz').get('foo')).toBe('baz');
   });
 
   it('in get(), throws an error if a key does not exist', () => {
     expect(() => new Cache().get('foo')).toThrow('The key foo does not exist');
-    expect(() => {
-      const cache = new Cache();
-      cache.set('foo', 'baz', 0, new Date().getTime() - 1);
-      cache.get('foo');
-    }).toThrow('The key foo does not exist');
+    expect(() =>
+      new Cache().set('foo', 'baz', 0, new Date().getTime() - 1).get('foo')
+    ).toThrow('The key foo does not exist');
   });
 
   it('gets whether it has a value', () => {
-    const cache = new Cache();
-    expect(cache.has('foo')).toBe(false);
-
-    cache.set('foo', 'baz');
-    expect(cache.has('foo')).toBe(true);
+    expect(new Cache().has('foo')).toBe(false);
+    expect(new Cache().set('foo', 'baz').has('foo')).toBe(true);
   });
 
   describe('cache respects key expiration', () => {
@@ -41,9 +34,9 @@ describe('Cache', () => {
       h: { val: 'lorem', exp: 0 },
       i: { val: 'lorem', exp: 0 },
       j: { val: 'lorem', exp: 0 },
-    });
-    cache.set('foo', 'ipsum');
-    cache.set('baz', 'another');
+    })
+      .set('foo', 'ipsum')
+      .set('baz', 'another');
 
     expect(cache.has('foo')).toBe(true);
     expect(cache.has('baz')).toBe(true);