diff --git a/server/stream.go b/server/stream.go
index 0e75aa49..0374fe6c 100644
--- a/server/stream.go
+++ b/server/stream.go
@@ -520,6 +520,8 @@ func (mset *Stream) Purge() uint64 {
 		return 0
 	}
 	purged := mset.store.Purge()
+	// Purge dedupe.
+	mset.ddmap = nil
 	stats := mset.store.State()
 	var obs []*Consumer
 	for _, o := range mset.consumers {
diff --git a/test/jetstream_test.go b/test/jetstream_test.go
index 485d1b2e..ee43f1d5 100644
--- a/test/jetstream_test.go
+++ b/test/jetstream_test.go
@@ -2896,6 +2896,10 @@ func TestJetStreamPublishDeDupe(t *testing.T) {
 	if !pa.Duplicate {
 		t.Fatalf("Expected duplicate to be set")
 	}
+
+	// Purge should wipe the msgIds as well.
+	mset.Purge()
+	nmids(0)
 }
 
 func TestJetStreamPullConsumerRemoveInterest(t *testing.T) {