diff --git a/src/main/java/com/pivovarit/collectors/CompletionOrderSpliterator.java b/src/main/java/com/pivovarit/collectors/CompletionOrderSpliterator.java
index 8ab52d94..6fc75eda 100644
--- a/src/main/java/com/pivovarit/collectors/CompletionOrderSpliterator.java
+++ b/src/main/java/com/pivovarit/collectors/CompletionOrderSpliterator.java
@@ -1,11 +1,12 @@
 package com.pivovarit.collectors;
 
-import java.util.List;
 import java.util.Spliterator;
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Consumer;
+import java.util.stream.Stream;
 
 /**
  * @author Grzegorz Piwowarek
@@ -16,10 +17,15 @@ final class CompletionOrderSpliterator<T> implements Spliterator<T> {
     private final BlockingQueue<CompletableFuture<T>> completed = new LinkedBlockingQueue<>();
     private int remaining;
 
-    CompletionOrderSpliterator(List<CompletableFuture<T>> futures) {
-        this.initialSize = futures.size();
+    CompletionOrderSpliterator(Stream<CompletableFuture<T>> futures) {
+        AtomicInteger size = new AtomicInteger();
+        futures.forEach(f -> {
+            f.whenComplete((__, ___) -> completed.add(f));
+            size.incrementAndGet();
+        });
+
+        this.initialSize = size.get();
         this.remaining = initialSize;
-        futures.forEach(f -> f.whenComplete((__, ___) -> completed.add(f)));
     }
 
     @Override
diff --git a/src/main/java/com/pivovarit/collectors/ParallelStreamCollector.java b/src/main/java/com/pivovarit/collectors/ParallelStreamCollector.java
index fecf0de9..2ce69b1b 100644
--- a/src/main/java/com/pivovarit/collectors/ParallelStreamCollector.java
+++ b/src/main/java/com/pivovarit/collectors/ParallelStreamCollector.java
@@ -29,18 +29,18 @@
 /**
  * @author Grzegorz Piwowarek
  */
-class ParallelStreamCollector<T, R> implements Collector<T, List<CompletableFuture<R>>, Stream<R>> {
+class ParallelStreamCollector<T, R> implements Collector<T, Stream.Builder<CompletableFuture<R>>, Stream<R>> {
 
     private static final EnumSet<Characteristics> UNORDERED = EnumSet.of(Characteristics.UNORDERED);
 
     private final Dispatcher<R> dispatcher;
     private final Function<T, R> function;
-    private final Function<List<CompletableFuture<R>>, Stream<R>> processor;
+    private final Function<Stream<CompletableFuture<R>>, Stream<R>> processor;
     private final Set<Characteristics> characteristics;
 
     private ParallelStreamCollector(
       Function<T, R> function,
-      Function<List<CompletableFuture<R>>, Stream<R>> processor,
+      Function<Stream<CompletableFuture<R>>, Stream<R>> processor,
       Set<Characteristics> characteristics,
       Dispatcher<R> dispatcher) {
         this.processor = processor;
@@ -56,12 +56,12 @@ private void startConsuming() {
     }
 
     @Override
-    public Supplier<List<CompletableFuture<R>>> supplier() {
-        return ArrayList::new;
+    public Supplier<Stream.Builder<CompletableFuture<R>>> supplier() {
+        return Stream::builder;
     }
 
     @Override
-    public BiConsumer<List<CompletableFuture<R>>, T> accumulator() {
+    public BiConsumer<Stream.Builder<CompletableFuture<R>>, T> accumulator() {
         return (acc, e) -> {
             startConsuming();
             acc.add(dispatcher.enqueue(() -> function.apply(e)));
@@ -69,17 +69,17 @@ public BiConsumer<List<CompletableFuture<R>>, T> accumulator() {
     }
 
     @Override
-    public BinaryOperator<List<CompletableFuture<R>>> combiner() {
+    public BinaryOperator<Stream.Builder<CompletableFuture<R>>> combiner() {
         return (left, right) -> {
             throw new UnsupportedOperationException();
         };
     }
 
     @Override
-    public Function<List<CompletableFuture<R>>, Stream<R>> finisher() {
+    public Function<Stream.Builder<CompletableFuture<R>>, Stream<R>> finisher() {
         return acc -> {
             dispatcher.stop();
-            return processor.apply(acc);
+            return processor.apply(acc.build());
         };
     }
 
@@ -116,12 +116,12 @@ public Set<Characteristics> characteristics() {
           : new ParallelStreamCollector<>(mapper, streamOrderedStrategy(), emptySet(), limiting(executor, parallelism));
     }
 
-    private static <R> Function<List<CompletableFuture<R>>, Stream<R>> streamInCompletionOrderStrategy() {
+    private static <R> Function<Stream<CompletableFuture<R>>, Stream<R>> streamInCompletionOrderStrategy() {
         return futures -> StreamSupport.stream(new CompletionOrderSpliterator<>(futures), false);
     }
 
-    private static <R> Function<List<CompletableFuture<R>>, Stream<R>> streamOrderedStrategy() {
-        return futures -> futures.stream().map(CompletableFuture::join);
+    private static <R> Function<Stream<CompletableFuture<R>>, Stream<R>> streamOrderedStrategy() {
+        return futures -> futures.map(CompletableFuture::join);
     }
 
     static final class BatchingCollectors {
diff --git a/src/test/java/com/pivovarit/collectors/CompletionOrderSpliteratorTest.java b/src/test/java/com/pivovarit/collectors/CompletionOrderSpliteratorTest.java
index 226b5a0a..a53efc25 100644
--- a/src/test/java/com/pivovarit/collectors/CompletionOrderSpliteratorTest.java
+++ b/src/test/java/com/pivovarit/collectors/CompletionOrderSpliteratorTest.java
@@ -33,7 +33,7 @@ void shouldTraverseInCompletionOrder() {
             f2.complete(1);
         });
         List<Integer> results = StreamSupport.stream(
-          new CompletionOrderSpliterator<>(futures), false)
+          new CompletionOrderSpliterator<>(futures.stream()), false)
           .collect(Collectors.toList());
 
         assertThat(results).containsExactly(3, 2, 1);
@@ -54,7 +54,7 @@ void shouldPropagateException() {
             f2.complete(1);
         });
         assertThatThrownBy(() -> StreamSupport.stream(
-          new CompletionOrderSpliterator<>(futures), false)
+          new CompletionOrderSpliterator<>(futures.stream()), false)
           .collect(Collectors.toList()))
           .isInstanceOf(CompletionException.class)
           .hasCauseExactlyInstanceOf(RuntimeException.class);
@@ -74,7 +74,7 @@ void shouldStreamInCompletionOrder() {
         List<CompletableFuture<Integer>> futures = asList(new CompletableFuture<>(), CompletableFuture
           .completedFuture(value));
 
-        Optional<Integer> result = StreamSupport.stream(new CompletionOrderSpliterator<>(futures), false).findAny();
+        Optional<Integer> result = StreamSupport.stream(new CompletionOrderSpliterator<>(futures.stream()), false).findAny();
 
         assertThat(result).contains(value);
     }
@@ -83,7 +83,7 @@ void shouldStreamInCompletionOrder() {
     void shouldNotConsumeOnEmpty() {
         List<CompletableFuture<Integer>> futures = Collections.emptyList();
 
-        Spliterator<Integer> spliterator = new CompletionOrderSpliterator<>(futures);
+        Spliterator<Integer> spliterator = new CompletionOrderSpliterator<>(futures.stream());
 
         ResultHolder<Integer> result = new ResultHolder<>();
         boolean consumed = spliterator.tryAdvance(result);