diff --git a/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java b/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java
index cb17582..3d56c50 100644
--- a/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java
+++ b/usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java
@@ -1970,10 +1970,20 @@ public class DeviceTest {
             } else {
                 usb.serialPort.getRI();
             }
-            fail("error expected");
+            fail("connection closed expected");
         } catch (IOException ignored) {
         } catch (UnsupportedOperationException ignored) {
         }
+        try {
+            usb.serialPort.getRI();
+            fail("connection closed expected");
+        } catch (IOException ignored) {
+        }
+        // reset error
+        usb.close(EnumSet.of(UsbWrapper.OpenCloseFlags.NO_CONTROL_LINE_INIT));
+        usb.open(EnumSet.of(UsbWrapper.OpenCloseFlags.NO_CONTROL_LINE_INIT, UsbWrapper.OpenCloseFlags.NO_IOMANAGER_THREAD));
+        usb.serialPort.getRI();
+        usb.serialPort.setRTS(true);
     }
 
     @Test
diff --git a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/CdcAcmSerialDriver.java b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/CdcAcmSerialDriver.java
index d158b80..02ae7a5 100644
--- a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/CdcAcmSerialDriver.java
+++ b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/CdcAcmSerialDriver.java
@@ -278,7 +278,7 @@ public class CdcAcmSerialDriver implements UsbSerialDriver {
         private void readControlLinesThreadFunction() {
             try {
                 byte[] buffer = new byte[Math.max(SERIAL_STATE_PACKET_SIZE, mControlEndpoint.getMaxPacketSize())];
-                while (!mStopReadControlLinesThread) {
+                while (!mStopReadControlLinesThread && mConnection!=null) {
                     long endTime = MonotonicClock.millis() + 500;
                     int readBytesCount = mConnection.bulkTransfer(mControlEndpoint, buffer, buffer.length, 500);
                     if (readBytesCount == -1) {
@@ -296,14 +296,14 @@ public class CdcAcmSerialDriver implements UsbSerialDriver {
                     Log.d(TAG, "control line state " + Arrays.toString(buffer));
                 }
             } catch (Exception e) {
-                if (isOpen()) {
-                    mReadControlLinesException = e;
-                }
+                mReadControlLinesException = e;
             }
         }
 
         private int getSerialState() throws IOException {
-            if ((mReadControlLinesThread == null) && (mReadControlLinesException == null)) {
+            if(mConnection == null)
+                throw new IOException("connection closed");
+            if (mReadControlLinesThread == null) {
                 synchronized (mReadControlLinesThreadLock) {
                     if (mReadControlLinesThread == null) {
                         mSerialState = 0;
@@ -313,17 +313,12 @@ public class CdcAcmSerialDriver implements UsbSerialDriver {
                     }
                 }
             }
-
-            Exception readControlLinesException = mReadControlLinesException;
-            if (readControlLinesException != null) {
-                mReadControlLinesException = null;
-                throw new IOException(readControlLinesException);
+            if (mReadControlLinesException != null) {
+                throw new IOException(mReadControlLinesException);
             }
-
             return mSerialState;
         }
 
-
         @Override
         protected void closeInt() {
             try {
diff --git a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/ProlificSerialDriver.java b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/ProlificSerialDriver.java
index 3041422..54362f6 100644
--- a/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/ProlificSerialDriver.java
+++ b/usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/ProlificSerialDriver.java
@@ -218,14 +218,13 @@ public class ProlificSerialDriver implements UsbSerialDriver {
                     }
                 }
             } catch (Exception e) {
-                if (isOpen())
-                    mReadStatusException = e;
+                mReadStatusException = e;
             }
             //Log.d(TAG, "end control line status thread " + mStopReadStatusThread + " " + (mReadStatusException == null ? "-" : mReadStatusException.getMessage()));
         }
 
         private int getStatus() throws IOException {
-            if ((mReadStatusThread == null) && (mReadStatusException == null)) {
+            if (mReadStatusThread == null) {
                 synchronized (mReadStatusThreadLock) {
                     if (mReadStatusThread == null) {
                         mStatus = 0;
@@ -249,14 +248,9 @@ public class ProlificSerialDriver implements UsbSerialDriver {
                     }
                 }
             }
-
-            /* throw and clear an exception which occurred in the status read thread */
-            Exception readStatusException = mReadStatusException;
             if (mReadStatusException != null) {
-                mReadStatusException = null;
-                throw new IOException(readStatusException);
+                throw new IOException(mReadStatusException);
             }
-
             return mStatus;
         }