diff --git a/test/typescript/custom-types/custom-types.d.ts b/test/typescript/custom-types/custom-types.d.ts
index 5fc5e8e4..ca7dbdf1 100644
--- a/test/typescript/custom-types/custom-types.d.ts
+++ b/test/typescript/custom-types/custom-types.d.ts
@@ -14,6 +14,13 @@ declare module 'react-i18next' {
           barfoo: 'barfoo';
         };
       };
+      plurals: {
+        foo_zero: 'foo';
+        foo_one: 'foo';
+        foo_two: 'foo';
+        foo_many: 'foo';
+        foo_other: 'foo';
+      };
     };
   }
 }
diff --git a/test/typescript/custom-types/useTranslation.test.tsx b/test/typescript/custom-types/useTranslation.test.tsx
index b2f0b300..9d6595e8 100644
--- a/test/typescript/custom-types/useTranslation.test.tsx
+++ b/test/typescript/custom-types/useTranslation.test.tsx
@@ -43,6 +43,16 @@ function keyPrefixOption() {
   return <>{t('barfoo')}</>;
 }
 
+function jsonFormatV4Plurals() {
+  const [t] = useTranslation('plurals');
+  return (
+    <>
+      {t('foo')}
+      {t('foo_one')}
+    </>
+  );
+}
+
 function expectErrorWhenNamespaceDoesNotExist() {
   // @ts-expect-error
   const [t] = useTranslation('fake');
diff --git a/ts4.1/index.d.ts b/ts4.1/index.d.ts
index 46603fc9..5f5bb61e 100644
--- a/ts4.1/index.d.ts
+++ b/ts4.1/index.d.ts
@@ -35,8 +35,10 @@ export interface Resources {}
  * declare module 'react-i18next' {
  *   interface CustomTypeOptions {
  *     defaultNS: 'custom';
- *     returnNull: false,
- *     returnEmptyString: false,
+ *     returnNull: false;
+ *     returnEmptyString: false;
+ *     keySeparator: '.';
+ *     jsonFormat: 'v4';
  *     resources: {
  *       custom: {
  *         foo: 'foo';
@@ -56,6 +58,7 @@ type TypeOptions = MergeBy<
     returnEmptyString: true;
     keySeparator: '.';
     defaultNS: 'translation';
+    jsonFormat: 'v4';
     resources: Resources;
   },
   CustomTypeOptions
@@ -92,6 +95,12 @@ declare module 'i18next' {
   }
 }
 
+type WithOrWithoutPlural<K> = TypeOptions['jsonFormat'] extends 'v4'
+  ? K extends `${infer B}_${'zero' | 'one' | 'two' | 'few' | 'many' | 'other'}`
+    ? B | K
+    : K
+  : K;
+
 // Normalize single namespace
 type AppendKeys<K1, K2, S extends string = TypeOptions['keySeparator']> = `${K1 & string}${S}${K2 &
   string}`;
@@ -100,11 +109,11 @@ type AppendKeys2<K1, K2, S extends string = TypeOptions['keySeparator']> = `${K1
 type Normalize2<T, K = keyof T> = K extends keyof T
   ? T[K] extends Record<string, any>
     ? T[K] extends readonly any[]
-      ? AppendKeys2<K, keyof T[K]> | AppendKeys2<K, Normalize2<T[K]>>
-      : AppendKeys<K, keyof T[K]> | AppendKeys<K, Normalize2<T[K]>>
+      ? AppendKeys2<K, WithOrWithoutPlural<keyof T[K]>> | AppendKeys2<K, Normalize2<T[K]>>
+      : AppendKeys<K, WithOrWithoutPlural<keyof T[K]>> | AppendKeys<K, Normalize2<T[K]>>
     : never
   : never;
-type Normalize<T> = keyof T | Normalize2<T>;
+type Normalize<T> = WithOrWithoutPlural<keyof T> | Normalize2<T>;
 
 // Normalize multiple namespaces
 type UnionToIntersection<U> = (U extends any ? (k: U) => void : never) extends (k: infer I) => void