diff --git a/pkg/channels/wecom/dedupe.go b/pkg/channels/wecom/dedupe.go
index 09f5a8a41..8ca98a30d 100644
--- a/pkg/channels/wecom/dedupe.go
+++ b/pkg/channels/wecom/dedupe.go
@@ -14,14 +14,18 @@ func markMessageProcessed(msgMu *sync.RWMutex, processedMsgs *map[string]bool, m
 	msgMu.Lock()
 	defer msgMu.Unlock()
 
+	if *processedMsgs == nil {
+		*processedMsgs = make(map[string]bool)
+	}
+
 	if (*processedMsgs)[msgID] {
 		return false
 	}
 	(*processedMsgs)[msgID] = true
 
-	// Keep existing behavior: when over limit, reset dedupe map entirely.
+	// When over limit, reset dedupe map but keep the current message.
 	if len(*processedMsgs) > maxEntries {
-		*processedMsgs = make(map[string]bool)
+		*processedMsgs = map[string]bool{msgID: true}
 	}
 
 	return true
diff --git a/pkg/channels/wecom_dedupe_test.go b/pkg/channels/wecom_dedupe_test.go
index 467f79979..71f987892 100644
--- a/pkg/channels/wecom_dedupe_test.go
+++ b/pkg/channels/wecom_dedupe_test.go
@@ -60,14 +60,19 @@ func TestMarkMessageProcessed_RotationClearsMapAtBoundary(t *testing.T) {
 		t.Fatalf("expected map size 1 after first insert, got %d", len(processed))
 	}
 
-	// Inserting second unique message exceeds maxEntries and should reset map.
+	// Inserting second unique message exceeds maxEntries and should reset map, but keep the new message.
 	if ok := markMessageProcessed(&mu, &processed, "msg-2", 1); !ok {
 		t.Fatalf("second unique message should be accepted")
 	}
-	if len(processed) != 0 {
-		t.Fatalf("expected map to be reset after rotation, got size %d", len(processed))
+	if len(processed) != 1 {
+		t.Fatalf("expected map to retain current message after rotation, got size %d", len(processed))
 	}
-	if processed["msg-2"] {
-		t.Fatalf("expected current message marker to be cleared after rotation")
+	if !processed["msg-2"] {
+		t.Fatalf("expected current message marker to be retained after rotation")
+	}
+
+	// Because msg-2 was retained, an immediate duplicate should be rejected.
+	if ok := markMessageProcessed(&mu, &processed, "msg-2", 1); ok {
+		t.Fatalf("duplicate message immediately after rotation should be rejected")
 	}
 }