diff --git a/src/builtin-entries.js b/src/builtin-entries.js
index f0cc65f94..5e13842e5 100644
--- a/src/builtin-entries.js
+++ b/src/builtin-entries.js
@@ -126,7 +126,7 @@ const cache = shared.memoize.builtinEntries
 
 for (const id of builtinIds) {
   setDeferred(builtinEntries, id, () => {
-    const cached = cache[id]
+    const cached = cache.get(id)
 
     if (cached) {
       return cached
@@ -135,7 +135,7 @@ for (const id of builtinIds) {
     const entry = createEntry(id)
 
     if (id !== "module") {
-      cache[id] = entry
+      cache.set(id, entry)
     }
 
     return entry
diff --git a/src/builtin-modules.js b/src/builtin-modules.js
index 5034f8e64..4935ee53e 100644
--- a/src/builtin-modules.js
+++ b/src/builtin-modules.js
@@ -34,7 +34,7 @@ function getExports(id) {
 
 for (const id of builtinIds) {
   setDeferred(builtinModules, id, () => {
-    const cached = cache[id]
+    const cached = cache.get(id)
 
     if (cached) {
       return cached
@@ -46,7 +46,7 @@ for (const id of builtinIds) {
     mod.loaded = true
 
     if (id !== "module") {
-      cache[id] = mod
+      cache.set(id, mod)
     }
 
     return mod
diff --git a/src/fs/realpath.js b/src/fs/realpath.js
index 221789eb3..c8e048321 100644
--- a/src/fs/realpath.js
+++ b/src/fs/realpath.js
@@ -28,7 +28,8 @@ function init() {
     }
 
     const cache = shared.memoize.fsRealpath
-    const cached = cache[thePath]
+
+    let cached = cache.get(thePath)
 
     if (cached) {
       return cached
@@ -44,9 +45,12 @@ function init() {
         typeof binding.fs.realpath === "function"
     }
 
-    return cache[thePath] = useBinding
+    cached = useBinding
       ? realpathBinding(thePath)
       : realpathFallback(thePath)
+
+    cache.set(thePath, cached)
+    return cached
   }
 
   function realpathBinding(thePath) {
diff --git a/src/module/esm/resolve-filename.js b/src/module/esm/resolve-filename.js
index 2610d4afa..177cb1e31 100644
--- a/src/module/esm/resolve-filename.js
+++ b/src/module/esm/resolve-filename.js
@@ -91,22 +91,21 @@ function resolveFilename(request, parent, isMain, options) {
     fromPath = ""
   }
 
+  const cache = shared.memoize.moduleESMResolveFilename
+
   let cacheKey
 
-  if (isObject(options)) {
-    cacheKey = ""
-  } else {
+  if (! isObject(options)) {
     cacheKey =
       request + "\0" +
       fromPath + "\0" +
       (isMain ? "1" : "")
-  }
 
-  const cache = shared.memoize.moduleESMResolveFilename
-  const cached = cacheKey && cache[cacheKey]
+    const cached = cache.get(cacheKey)
 
-  if (cached) {
-    return cached
+    if (cached) {
+      return cached
+    }
   }
 
   if (isAbs) {
@@ -172,7 +171,8 @@ function resolveFilename(request, parent, isMain, options) {
 
     if (! foundPath &&
         Reflect.has(builtinLookup, decoded)) {
-      return cache[cacheKey] = decoded
+      cache.set(cacheKey, decoded)
+      return decoded
     }
   }
 
@@ -183,7 +183,8 @@ function resolveFilename(request, parent, isMain, options) {
         isJS(foundPath) ||
         isMJS(foundPath) ||
         Reflect.has(strictExtsLookup, extname(foundPath))) {
-      return cache[cacheKey] = foundPath
+      cache.set(cacheKey, foundPath)
+      return foundPath
     }
 
     throw new ERR_UNKNOWN_FILE_EXTENSION(foundPath)
diff --git a/src/module/internal/find-path.js b/src/module/internal/find-path.js
index 8055cc84e..6d16cc3da 100644
--- a/src/module/internal/find-path.js
+++ b/src/module/internal/find-path.js
@@ -55,7 +55,7 @@ function findPath(request, paths, isMain, fields, exts) {
   }
 
   const cache = shared.memoize.moduleInternalFindPath
-  const cached = cache[cacheKey]
+  const cached = cache.get(cacheKey)
 
   if (cached !== void 0) {
     return cached
@@ -172,7 +172,8 @@ function findPath(request, paths, isMain, fields, exts) {
     }
 
     if (filename) {
-      return cache[cacheKey] = filename
+      cache.set(cacheKey, filename)
+      return filename
     }
   }
 
diff --git a/src/module/internal/read-package.js b/src/module/internal/read-package.js
index 13d7845b0..38fd92a91 100644
--- a/src/module/internal/read-package.js
+++ b/src/module/internal/read-package.js
@@ -1,4 +1,5 @@
 import GenericArray from "../../generic/array.js"
+import GenericObject from "../../generic/object.js"
 import SafeJSON from "../../safe/json.js"
 
 import readFileFast from "../../fs/read-file-fast.js"
@@ -18,8 +19,10 @@ function readPackage(dirPath, fields) {
     cacheKey += "\0" + (fieldsLength === 1 ? fields[0] : GenericArray.join(fields))
   }
 
-  if (Reflect.has(cache, cacheKey)) {
-    return cache[cacheKey]
+  let cached = cache.get(cacheKey)
+
+  if (cached) {
+    return cached
   }
 
   const jsonPath = dirPath + sep + "package.json"
@@ -33,12 +36,17 @@ function readPackage(dirPath, fields) {
   }
 
   try {
-    return cache[cacheKey] = SafeJSON.parse(jsonString)
+    cached =
+      SafeJSON.parse(jsonString) ||
+      GenericObject.create()
   } catch (e) {
     e.path = jsonPath
     e.message = "Error parsing " + jsonPath + ": " + toString(e.message)
     throw e
   }
+
+  cache.set(cacheKey, cached)
+  return cached
 }
 
 export default readPackage
diff --git a/src/module/static/resolve-filename.js b/src/module/static/resolve-filename.js
index cd79f1754..5b4434b45 100644
--- a/src/module/static/resolve-filename.js
+++ b/src/module/static/resolve-filename.js
@@ -61,22 +61,21 @@ function resolveFilename(request, parent, isMain, options) {
     fromPath = ""
   }
 
+  const cache = shared.memoize.moduleStaticResolveFilename
+
   let cacheKey
 
-  if (isObject(options)) {
-    cacheKey = ""
-  } else {
+  if (! isObject(options)) {
     cacheKey =
       request + "\0" +
       fromPath + "\0" +
       (isMain ? "1" : "")
-  }
 
-  const cache = shared.memoize.moduleStaticResolveFilename
-  const cached = cacheKey && cache[cacheKey]
+    const cached = cache.get(cacheKey)
 
-  if (cached) {
-    return cached
+    if (cached) {
+      return cached
+    }
   }
 
   if (isAbs) {
@@ -102,9 +101,11 @@ function resolveFilename(request, parent, isMain, options) {
   const foundPath = Module._findPath(request, paths, isMain)
 
   if (foundPath) {
-    return cacheKey
-      ? cache[cacheKey] = foundPath
-      : foundPath
+    if (cacheKey) {
+      cache.set(cacheKey, foundPath)
+    }
+
+    return foundPath
   }
 
   throw new MODULE_NOT_FOUND(request)
diff --git a/src/shared.js b/src/shared.js
index faf0bcabf..b6b411956 100644
--- a/src/shared.js
+++ b/src/shared.js
@@ -62,21 +62,21 @@ function init() {
     external: __external__,
     inited: false,
     memoize: {
-      builtinEntries: { __proto__: null },
-      builtinModules: { __proto__: null },
-      fsRealpath: { __proto__: null },
-      moduleESMResolveFilename: { __proto__: null },
-      moduleInternalFindPath: { __proto__: null },
-      moduleInternalReadPackage: { __proto__: null },
-      moduleStaticResolveFilename: { __proto__: null },
+      builtinEntries: new Map,
+      builtinModules: new Map,
+      fsRealpath: new Map,
+      moduleESMResolveFilename: new Map,
+      moduleInternalFindPath: new Map,
+      moduleInternalReadPackage: new Map,
+      moduleStaticResolveFilename: new Map,
       shimFunctionPrototypeToString: new WeakMap,
       shimProcessBindingUtilGetProxyDetails: new WeakMap,
       utilGetProxyDetails: new WeakMap,
       utilMaskFunction: new WeakMap,
-      utilMaxSatisfying: { __proto__: null },
-      utilParseURL: { __proto__: null },
+      utilMaxSatisfying: new Map,
+      utilParseURL: new Map,
       utilProxyExports: new WeakMap,
-      utilSatisfies: { __proto__: null },
+      utilSatisfies: new Map,
       utilUnwrapOwnProxy: new WeakMap,
       utilUnwrapProxy: new WeakMap
     },
diff --git a/src/util/max-satisfying.js b/src/util/max-satisfying.js
index 8a65753e5..a2403015b 100644
--- a/src/util/max-satisfying.js
+++ b/src/util/max-satisfying.js
@@ -16,11 +16,15 @@ function init() {
       range
 
     const cache = shared.memoize.utilMaxSatisfying
-    const cached = cache[cacheKey]
 
-    return cached === void 0
-      ? cache[cacheKey] = _maxSatisfying(versions, range)
-      : cached
+    let cached = cache.get(cacheKey)
+
+    if (cached === void 0) {
+      cached = _maxSatisfying(versions, range)
+      cache.set(cacheKey, cached)
+    }
+
+    return cached
   }
 
   return maxSatisfying
diff --git a/src/util/parse-url.js b/src/util/parse-url.js
index 240cb2756..dff8e650c 100644
--- a/src/util/parse-url.js
+++ b/src/util/parse-url.js
@@ -27,7 +27,14 @@ function init() {
     const cacheKey = typeof url === "string" ? url : ""
     const cache = shared.memoize.utilParseURL
 
-    return cache[cacheKey] || (cache[cacheKey] = parse(url))
+    let cached = cache.get(cacheKey)
+
+    if (cached === void 0) {
+      cached = parse(url)
+      cache.set(cacheKey, cached)
+    }
+
+    return cached
   }
 
   return parseURL
diff --git a/src/util/satisfies.js b/src/util/satisfies.js
index 2326d4158..6d7589ff6 100644
--- a/src/util/satisfies.js
+++ b/src/util/satisfies.js
@@ -11,11 +11,15 @@ function init() {
 
     const cacheKey = version + "\0" + range
     const cache = shared.memoize.utilSatisfies
-    const cached = cache[cacheKey]
 
-    return cached === void 0
-      ? cache[cacheKey] = _satisfies(stripPrereleaseTag(version), range)
-      : cached
+    let cached = cache.get(cacheKey)
+
+    if (cached === void 0) {
+      cached = _satisfies(stripPrereleaseTag(version), range)
+      cache.set(cacheKey, cached)
+    }
+
+    return cached
   }
 
   return satisfies