diff --git a/lib/memoization.js b/lib/memoization.js
index 2d2837a..abbab9b 100644
--- a/lib/memoization.js
+++ b/lib/memoization.js
@@ -5,43 +5,45 @@ const LRU = require('lru-cache')
 const MAX_SIZE = 50 * 1024 * 1024 // 50MB
 const MAX_AGE = 3 * 60 * 1000
 
-let MEMOIZED
-clearMemoized()
+let MEMOIZED = new LRU({
+  max: MAX_SIZE,
+  maxAge: MAX_AGE,
+  length: (entry, key) => {
+    if (key.startsWith('key:')) {
+      return entry.data.length
+    } else if (key.startsWith('digest:')) {
+      return entry.length
+    }
+  }
+})
 
 module.exports.clearMemoized = clearMemoized
 function clearMemoized () {
-  var old = MEMOIZED
-  MEMOIZED = new LRU({
-    max: MAX_SIZE,
-    maxAge: MAX_AGE,
-    length: (entry, key) => {
-      if (key.startsWith('key:')) {
-        return entry.data.length
-      } else if (key.startsWith('digest:')) {
-        return entry.length
-      }
-    }
+  const old = {}
+  MEMOIZED.forEach((v, k) => {
+    old[k] = v
   })
+  MEMOIZED.reset()
   return old
 }
 
 module.exports.put = put
 function put (cache, entry, data) {
-  MEMOIZED[`key:${cache}:${entry.key}`] = { entry, data }
+  MEMOIZED.set(`key:${cache}:${entry.key}`, { entry, data })
   putDigest(cache, entry.integrity, data)
 }
 
 module.exports.put.byDigest = putDigest
 function putDigest (cache, integrity, data) {
-  MEMOIZED[`digest:${cache}:${integrity}`] = data
+  MEMOIZED.set(`digest:${cache}:${integrity}`, data)
 }
 
 module.exports.get = get
 function get (cache, key) {
-  return MEMOIZED[`key:${cache}:${key}`]
+  return MEMOIZED.get(`key:${cache}:${key}`)
 }
 
 module.exports.get.byDigest = getDigest
 function getDigest (cache, integrity) {
-  return MEMOIZED[`digest:${cache}:${integrity}`]
+  return MEMOIZED.get(`digest:${cache}:${integrity}`)
 }