diff --git a/src/main/java/io/reactivex/rxjava3/core/Flowable.java b/src/main/java/io/reactivex/rxjava3/core/Flowable.java
index 4d277ab08b..8bb6156659 100644
--- a/src/main/java/io/reactivex/rxjava3/core/Flowable.java
+++ b/src/main/java/io/reactivex/rxjava3/core/Flowable.java
@@ -20394,7 +20394,7 @@ public final TestSubscriber<T> test(long initialRequest, boolean cancel) { // No
     @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <@NonNull R, @NonNull A> Single<R> collect(@NonNull Collector<? super T, A, R> collector) {
+    public final <@NonNull R, @Nullable A> Single<R> collect(@NonNull Collector<? super T, A, R> collector) {
         Objects.requireNonNull(collector, "collector is null");
         return RxJavaPlugins.onAssembly(new FlowableCollectWithCollectorSingle<>(this, collector));
     }