diff --git a/src/system/iterable.ts b/src/system/iterable.ts
index 4b7ee70..df02f8b 100644
--- a/src/system/iterable.ts
+++ b/src/system/iterable.ts
@@ -38,12 +38,12 @@ export function* chunkByStringLength(source: string[], maxLength: number): Itera
 	}
 }
 
-export function count<T>(source: Iterable<T> | IterableIterator<T>, predicate?: (item: T) => boolean): number {
+export function count<T>(source: IterableIterator<T>, predicate?: (item: T) => boolean): number {
 	let count = 0;
 	let next: IteratorResult<T>;
 
 	while (true) {
-		next = (source as IterableIterator<T>).next();
+		next = source.next();
 		if (next.done) break;
 
 		if (predicate === undefined || predicate(next.value)) {
diff --git a/src/system/searchTree.ts b/src/system/searchTree.ts
index a4bc2a3..b76e98b 100644
--- a/src/system/searchTree.ts
+++ b/src/system/searchTree.ts
@@ -380,7 +380,7 @@ export class TernarySearchTree<K, V> {
 		return count(this.entries(), predicate === undefined ? undefined : ([, e]) => predicate(e));
 	}
 
-	entries(): Iterable<[K, V]> {
+	entries(): IterableIterator<[K, V]> {
 		return this._iterator(this._root);
 	}
 
@@ -391,7 +391,7 @@ export class TernarySearchTree<K, V> {
 	highlander(): [K, V] | undefined {
 		if (this._root === undefined || this._root.isEmpty()) return undefined;
 
-		const entries = this.entries() as IterableIterator<[K, V]>;
+		const entries = this.entries();
 
 		let count = 0;
 		let next: IteratorResult<[K, V]>;