diff --git a/reactor-core/src/main/java/reactor/core/publisher/FluxWindowTimeout.java b/reactor-core/src/main/java/reactor/core/publisher/FluxWindowTimeout.java
index a2381575f9..304e9af382 100644
--- a/reactor-core/src/main/java/reactor/core/publisher/FluxWindowTimeout.java
+++ b/reactor-core/src/main/java/reactor/core/publisher/FluxWindowTimeout.java
@@ -184,6 +184,11 @@ public void onNext(T t) {
 				}
 
 				final InnerWindow<T> window = this.window;
+				if (window == null) {
+					Operators.onDiscard(t, this.actual.currentContext());
+					return;
+				}
+
 				if (window.sendNext(t)) {
 					return;
 				}