diff --git a/n2kMapper.js b/n2kMapper.js
index 6f2bfa3..e82f027 100644
--- a/n2kMapper.js
+++ b/n2kMapper.js
@@ -190,8 +190,8 @@ var toDelta = function (n2k, state, customPgns = {}) {
         //filter out invalid mmsi
         let last = result.context.lastIndexOf(':')
         if ( last != -1 && result.context.slice(last+1).length < 9 ) {
-          console.log('BAD: ' + result.context)
-          result.updates = []
+          console.error('bad MMSI: ' + result.context)
+          return
         }
       }
 
diff --git a/test/129038_ais_class_a.js b/test/129038_ais_class_a.js
index c6f7629..19dfbe4 100644
--- a/test/129038_ais_class_a.js
+++ b/test/129038_ais_class_a.js
@@ -80,7 +80,8 @@ describe('129038 Class A Update', function () {
       "description": "AIS Class A Position Report",
       "timestamp": "2022-05-09T13:38:38.917Z"
     }
-    mapper.toDelta(msg, {}).updates.length.should.equal(0)
+    const deltaType = typeof mapper.toDelta(msg, {})
+    deltaType.should.equal('undefined')
   })
 })