diff --git a/src/main/java/info/istlab/IoTP/SerialChecker.java b/src/main/java/info/istlab/IoTP/SerialChecker.java
index 95bec76..6d3a042 100644
--- a/src/main/java/info/istlab/IoTP/SerialChecker.java
+++ b/src/main/java/info/istlab/IoTP/SerialChecker.java
@@ -124,6 +124,7 @@
         for (SerialPort sp : ports) {
             String name = sp.getSystemPortName();
             if (name.startsWith("cu.usbserial") || name.startsWith("COM")) {
+                if (invalidSerialNames.containsKey(name)) continue;
                 validSerialNames.add(name);
                 portHash.put(name, sp);
             }