diff --git a/package.json b/package.json
index 8d6eb57..5ec307b 100644
--- a/package.json
+++ b/package.json
@@ -80,7 +80,6 @@
   "dependencies": {
     "commander": "^4.0.1",
     "estree-walker": "^0.9.0",
-    "fast-memoize": "^2.5.1",
     "intl-messageformat": "^7.5.2",
     "tiny-glob": "^0.2.6"
   }
diff --git a/src/client/includes/formatters.ts b/src/client/includes/formatters.ts
index 35b226b..babcbbf 100644
--- a/src/client/includes/formatters.ts
+++ b/src/client/includes/formatters.ts
@@ -1,10 +1,11 @@
 import IntlMessageFormat from 'intl-messageformat'
-import memoize from 'fast-memoize'
 
 import { MemoizedIntlFormatter } from '../types'
 import { getCurrentLocale } from '../stores/locale'
 import { getOptions } from '../configs'
 
+import { monadicMemoize } from './memoize'
+
 const getIntlFormatterOptions = (
   type: 'time' | 'number' | 'date',
   name: string
@@ -20,7 +21,7 @@ const getIntlFormatterOptions = (
 export const getNumberFormatter: MemoizedIntlFormatter<
   Intl.NumberFormat,
   Intl.NumberFormatOptions
-> = memoize(({ locale, format, ...options } = {}) => {
+> = monadicMemoize(({ locale, format, ...options } = {}) => {
   locale = locale || getCurrentLocale()
   if (locale == null) {
     throw new Error('[svelte-i18n] A "locale" must be set to format numbers')
@@ -36,7 +37,7 @@ export const getNumberFormatter: MemoizedIntlFormatter<
 export const getDateFormatter: MemoizedIntlFormatter<
   Intl.DateTimeFormat,
   Intl.DateTimeFormatOptions
-> = memoize(({ locale, format, ...options } = {}) => {
+> = monadicMemoize(({ locale, format, ...options } = {}) => {
   locale = locale || getCurrentLocale()
   if (locale == null) {
     throw new Error('[svelte-i18n] A "locale" must be set to format dates')
@@ -53,7 +54,7 @@ export const getDateFormatter: MemoizedIntlFormatter<
 export const getTimeFormatter: MemoizedIntlFormatter<
   Intl.DateTimeFormat,
   Intl.DateTimeFormatOptions
-> = memoize(({ locale, format, ...options } = {}) => {
+> = monadicMemoize(({ locale, format, ...options } = {}) => {
   locale = locale || getCurrentLocale()
   if (locale == null) {
     throw new Error(
@@ -69,7 +70,7 @@ export const getTimeFormatter: MemoizedIntlFormatter<
   return new Intl.DateTimeFormat(locale, options)
 })
 
-export const getMessageFormatter = memoize(
+export const getMessageFormatter = monadicMemoize(
   (message: string, locale: string = getCurrentLocale()) =>
     new IntlMessageFormat(message, locale, getOptions().formats)
 )
diff --git a/src/client/includes/memoize.ts b/src/client/includes/memoize.ts
new file mode 100644
index 0000000..956ffc6
--- /dev/null
+++ b/src/client/includes/memoize.ts
@@ -0,0 +1,14 @@
+type MemoizedFunction = <F extends any>(fn: F) => F
+
+const monadicMemoize: MemoizedFunction = fn => {
+  const cache = Object.create(null)
+  const memoizedFn: any = (arg: unknown) => {
+    const cacheKey = JSON.stringify(arg)
+    if (cacheKey in cache) {
+      return cache[cacheKey]
+    }
+    return (cache[cacheKey] = fn(arg))
+  }
+  return memoizedFn
+}
+export { monadicMemoize }
diff --git a/yarn.lock b/yarn.lock
index 7140506..04511ac 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2382,11 +2382,6 @@ fast-levenshtein@~2.0.6:
   resolved "https://registry.yarnpkg.com/fast-levenshtein/-/fast-levenshtein-2.0.6.tgz#3d8a5c66883a16a30ca8643e851f19baa7797917"
   integrity sha1-PYpcZog6FqMMqGQ+hR8Zuqd5eRc=
 
-fast-memoize@^2.5.1:
-  version "2.5.1"
-  resolved "https://registry.yarnpkg.com/fast-memoize/-/fast-memoize-2.5.1.tgz#c3519241e80552ce395e1a32dcdde8d1fd680f5d"
-  integrity sha512-xdmw296PCL01tMOXx9mdJSmWY29jQgxyuZdq0rEHMu+Tpe1eOEtCycoG6chzlcrWsNgpZP7oL8RiQr7+G6Bl6g==
-
 fb-watchman@^2.0.0:
   version "2.0.1"
   resolved "https://registry.yarnpkg.com/fb-watchman/-/fb-watchman-2.0.1.tgz#fc84fb39d2709cf3ff6d743706157bb5708a8a85"