diff --git a/reactor-core/src/main/java/reactor/core/publisher/FluxBufferTimeout.java b/reactor-core/src/main/java/reactor/core/publisher/FluxBufferTimeout.java
index a0c6648832..6fa695d19e 100644
--- a/reactor-core/src/main/java/reactor/core/publisher/FluxBufferTimeout.java
+++ b/reactor-core/src/main/java/reactor/core/publisher/FluxBufferTimeout.java
@@ -301,6 +301,14 @@ public void onNext(T t) {
 				// flushes. However, timeout does not reset it to 0, it has its own
 				// flag.
 				boolean terminated = false;
+				if (terminated) {
+					previousState = forceAddWork(this, BufferTimeoutWithBackpressureSubscriber::setTerminated);
+				} else {
+					previousState = forceAddWork(this, state -> incrementIndex(state, 1));
+				}
+				// We can only fire the timer once we increment the index first so that
+				// the timer doesn't fire first as it would consume the element and try
+				// to decrement the index below 0.
 				if (getIndex(previousState) == 0) {
 					// fire timer, new buffer starts
 					try {
@@ -312,11 +320,6 @@ public void onNext(T t) {
 						terminated = true;
 					}
 				}
-				if (terminated) {
-					previousState = forceAddWork(this, BufferTimeoutWithBackpressureSubscriber::setTerminated);
-				} else {
-					previousState = forceAddWork(this, state -> incrementIndex(state, 1));
-				}
 			} else {
 				previousState = forceAddWork(this, BufferTimeoutWithBackpressureSubscriber::setTerminated);
 			}
@@ -469,8 +472,6 @@ private void drain(boolean resumeDemand) {
 					}
 
 					if (terminated && queue.isEmpty()) {
-						// TODO: make sure we don't do this unless we
-						//  know all the values were delivered first
 						done = true;
 						if (logger != null) {
 							trace(logger, "terminated! error: " + this.error + " queue size: " + queue.size());
@@ -489,10 +490,6 @@ private void drain(boolean resumeDemand) {
 						previousState = resetTimeout(incrementIndex(previousState, toDecrement));
 					}
 
-					// TODO: If we force an update before we lose the knowledge that
-					//  some other actor modified something in between, so we must make
-					//  sure to track these updates in both current and previous and
-					//  compare.
 					currentState = tryClearWip(this, previousState);
 
 					// If the state changed (e.g. new item arrived, a request was issued,
@@ -581,8 +578,7 @@ private static long incrementRequestIndex(long state) {
 		}
 
 		private static long getIndex(long state) {
-			long l = (state & INDEX_MASK) >> INDEX_SHIFT;
-			return l;
+			return (state & INDEX_MASK) >> INDEX_SHIFT;
 		}
 
 		private static long incrementIndex(long state, int amount) {
@@ -605,10 +601,6 @@ private static long resetTimeout(long state) {
 			return state & ~TIMEOUT_FLAG;
 		}
 
-		private static long resetIndex(long state) {
-			return state & ~INDEX_MASK;
-		}
-
 		private static boolean isTimedOut(long state) {
 			return (state & TIMEOUT_FLAG) == TIMEOUT_FLAG;
 		}
@@ -666,7 +658,8 @@ private static <T, C extends Collection<? super T>> long tryClearWip(BufferTimeo
 					return currentState;
 				}
 
-				long nextState = currentState & ~HAS_WORK_IN_PROGRESS_FLAG;
+				// remove both WIP and requested_index so that we avoid overflowing
+				long nextState = currentState & ~HAS_WORK_IN_PROGRESS_FLAG & ~REQUESTED_INDEX_MASK;
 				if (STATE.compareAndSet(instance, currentState, nextState)) {
 					if (instance.stateLogger != null) {
 						instance.stateLogger.log(instance.toString(),