diff --git a/source/merge-deep.d.ts b/source/merge-deep.d.ts
index 31f1f3b28..7fed3b93f 100644
--- a/source/merge-deep.d.ts
+++ b/source/merge-deep.d.ts
@@ -63,6 +63,9 @@ type MergeDeepRecord<
 > = DoMergeDeepRecord<OmitIndexSignature<Destination>, OmitIndexSignature<Source>, Options>
 & Merge<PickIndexSignature<Destination>, PickIndexSignature<Source>>;
 
+// Helper to avoid computing ArrayTail twice.
+type PickRestTypeHelper<Tail extends UnknownArrayOrTuple, Type> = Tail extends [] ? Type : PickRestType<Tail>;
+
 /**
 Pick the rest type.
 
@@ -76,9 +79,18 @@ type Rest5 = PickRestType<string[]>; // => string[]
 ```
 */
 type PickRestType<Type extends UnknownArrayOrTuple> = number extends Type['length']
-	? ArrayTail<Type> extends [] ? Type : PickRestType<ArrayTail<Type>>
+	? PickRestTypeHelper<ArrayTail<Type>, Type>
 	: [];
 
+// Helper to avoid computing ArrayTail twice.
+type OmitRestTypeHelper<
+	Tail extends UnknownArrayOrTuple,
+	Type extends UnknownArrayOrTuple,
+	Result extends UnknownArrayOrTuple = [],
+> = Tail extends []
+	? Result
+	: OmitRestType<Tail, [...Result, FirstArrayElement<Type>]>;
+
 /**
 Omit the rest type.
 
@@ -93,7 +105,7 @@ type Tuple6 = OmitRestType<string[]>; // => []
 ```
 */
 type OmitRestType<Type extends UnknownArrayOrTuple, Result extends UnknownArrayOrTuple = []> = number extends Type['length']
-	? ArrayTail<Type> extends [] ? Result : OmitRestType<ArrayTail<Type>, [...Result, FirstArrayElement<Type>]>
+	? OmitRestTypeHelper<ArrayTail<Type>, Type, Result>
 	: Type;
 
 // Utility to avoid picking two times the type.