diff --git a/backend/src/api/websocket-handler.ts b/backend/src/api/websocket-handler.ts
index 34d4682d2..937d4a7c5 100644
--- a/backend/src/api/websocket-handler.ts
+++ b/backend/src/api/websocket-handler.ts
@@ -968,7 +968,7 @@ class WebsocketHandler {
         if (client['track-tx']) {
           numTxSubs++;
         }
-        if (client['track-mempool-block'] >= 0) {
+        if (client['track-mempool-block'] != null && client['track-mempool-block'] >= 0) {
           numProjectedSubs++;
         }
         if (client['track-rbf']) {