diff --git a/SerialInjectGPS.cs b/SerialInjectGPS.cs
index e7b5ee12c4..ada40ec5d2 100644
--- a/SerialInjectGPS.cs
+++ b/SerialInjectGPS.cs
@@ -132,6 +132,8 @@ private void Rtcm3_ObsMessage(object sender, EventArgs e)
             {
                 List<rtcm3.ob> obs = sender as List<rtcm3.ob>;
 
+                if (obs.Count == 0) return;
+				
                 // get system controls
                 Func<char,List<VerticalProgressBar2>> ctls = delegate (char sys)
                 {