diff --git a/TODO.md b/TODO.md
index f805dcb..7e6de2c 100644
--- a/TODO.md
+++ b/TODO.md
@@ -33,6 +33,9 @@ tested.
 
 # Completed Steps
 
+- 2026-10-27: once the stop deadline has passed, the prefix handler starts no
+  flush. A batch that filled while a write ran past the deadline could still be
+  written after it (closes #188)
 - 2026-10-27: the prefix handler applies each update to the routing table in
   memory, and writes the table's changes to the database every second. A write
   takes at most 20,000 changed pairs, and the rest follow in the next writes. A
diff --git a/internal/routewatch/batchwrite_internal_test.go b/internal/routewatch/batchwrite_internal_test.go
index 42c16bc..d6c369a 100644
--- a/internal/routewatch/batchwrite_internal_test.go
+++ b/internal/routewatch/batchwrite_internal_test.go
@@ -351,6 +351,31 @@ func TestPrefixHandlerSkipsItsLastWriteAfterTheStopDeadline(t *testing.T) {
 	}
 }
 
+// TestPrefixHandlerSkipsAFullBatchAfterTheStopDeadline hands the prefix handler
+// a full batch while a write is held, so the batch's wake-up of the flush
+// goroutine waits. The stop deadline passes meanwhile. When the write ends, the
+// flush goroutine must stop instead of writing the batch.
+func TestPrefixHandlerSkipsAFullBatchAfterTheStopDeadline(t *testing.T) {
+	t.Parallel()
+
+	const extraPrefix = "198.51.100.0/24"
+
+	store := newBlockingStore()
+	h := NewPrefixHandler(store, logger.New(), routetable.New(routetable.Params{}))
+	fill := slices.Repeat([]string{testV4Prefix}, prefixBatchSize)
+	full := slices.Repeat([]string{extraPrefix}, prefixBatchSize)
+	stopWhileAWriteIsBlocked(t, store, h, h.done,
+		[]*ristypes.RISMessage{prefixAnnouncement(fill)},
+		prefixAnnouncement(full))
+
+	store.mu.Lock()
+	defer store.mu.Unlock()
+
+	if store.prefixes[extraPrefix] {
+		t.Errorf("%s was written after the stop deadline", extraPrefix)
+	}
+}
+
 // tableWriteBlockingStore is a blockingStore whose writes of the routing
 // table's changes also wait until the test calls releaseWrites.
 type tableWriteBlockingStore struct {
diff --git a/internal/routewatch/prefixhandler.go b/internal/routewatch/prefixhandler.go
index c2764cf..d68d593 100644
--- a/internal/routewatch/prefixhandler.go
+++ b/internal/routewatch/prefixhandler.go
@@ -323,6 +323,21 @@ func (h *PrefixHandler) flushLoop() {
 	defer ticker.Stop()
 
 	for {
+		// Stop goes first. A write can run past the stop deadline while a full
+		// batch's wake-up or a tick waits beside Stop's context. The select
+		// below picks one of them at random, but past the deadline no flush
+		// may start.
+		select {
+		case ctx := <-h.stopCh:
+			// Final flush, unless the stop deadline has passed
+			if ctx.Err() == nil {
+				h.flushBatch()
+			}
+
+			return
+		default:
+		}
+
 		select {
 		case <-ticker.C:
 			if time.Since(h.lastFlush) >= prefixBatchTimeout {