diff --git a/usbserial/src/main/java/com/felhr/usbserial/CH34xSerialDevice.java b/usbserial/src/main/java/com/felhr/usbserial/CH34xSerialDevice.java
index a316572..80bb911 100644
--- a/usbserial/src/main/java/com/felhr/usbserial/CH34xSerialDevice.java
+++ b/usbserial/src/main/java/com/felhr/usbserial/CH34xSerialDevice.java
@@ -583,7 +583,8 @@ public class CH34xSerialDevice extends UsbSerialDevice
 
     private void startFlowControlThread()
     {
-        flowControlThread.start();
+        if(!flowControlThread.isAlive())
+            flowControlThread.start();
     }
 
     private void stopFlowControlThread()
diff --git a/usbserial/src/main/java/com/felhr/usbserial/CP2102SerialDevice.java b/usbserial/src/main/java/com/felhr/usbserial/CP2102SerialDevice.java
index b3658c6..9b9961b 100644
--- a/usbserial/src/main/java/com/felhr/usbserial/CP2102SerialDevice.java
+++ b/usbserial/src/main/java/com/felhr/usbserial/CP2102SerialDevice.java
@@ -513,7 +513,8 @@ public class CP2102SerialDevice extends UsbSerialDevice
 
     private void startFlowControlThread()
     {
-        flowControlThread.start();
+        if(!flowControlThread.isAlive())
+            flowControlThread.start();
     }
 
     private void stopFlowControlThread()