diff --git a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/securitytoken/SecurityTokenHelper.java b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/securitytoken/SecurityTokenHelper.java
index cedfc9514..878bf9df3 100644
--- a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/securitytoken/SecurityTokenHelper.java
+++ b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/securitytoken/SecurityTokenHelper.java
@@ -56,6 +56,7 @@ public class SecurityTokenHelper {
     private static final int MAX_APDU_NE_EXT = 65536;
 
     private static final int APDU_SW_SUCCESS = 0x9000;
+    private static final int APDU_SW1_RESPONSE_AVAILABLE = 0x61;
 
     private static final int MASK_CLA_CHAINING = 1 << 4;
 
@@ -530,7 +531,7 @@ public class SecurityTokenHelper {
         result.write(lastResponse.getData());
 
         // Receive
-        while (lastResponse.getSW1() == 0x61) {
+        while (lastResponse.getSW1() == APDU_SW1_RESPONSE_AVAILABLE) {
             // GET RESPONSE ISO/IEC 7816-4 par.7.6.1
             CommandAPDU getResponse = new CommandAPDU(0x00, 0xC0, 0x00, 0x00, lastResponse.getSW2());
             lastResponse = mTransport.transceive(getResponse);
diff --git a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/securitytoken/usb/CcidTransceiver.java b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/securitytoken/usb/CcidTransceiver.java
index acb1ca9f4..bf6711474 100644
--- a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/securitytoken/usb/CcidTransceiver.java
+++ b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/securitytoken/usb/CcidTransceiver.java
@@ -152,7 +152,7 @@ public class CcidTransceiver {
         }
     }
 
-    private byte getStatus(byte[] bytes) {
+    private static byte getStatus(byte[] bytes) {
         return (byte) ((bytes[7] >> 6) & 0x03);
     }
 
@@ -163,7 +163,7 @@ public class CcidTransceiver {
         }
     }
 
-    private boolean isDataBlockNotReady(byte[] bytes) {
+    private static boolean isDataBlockNotReady(byte[] bytes) {
         return getStatus(bytes) == 2;
     }
 }
diff --git a/OpenKeychain/src/main/res/xml/usb_device_filter.xml b/OpenKeychain/src/main/res/xml/usb_device_filter.xml
index 4532b928b..5db692bf6 100644
--- a/OpenKeychain/src/main/res/xml/usb_device_filter.xml
+++ b/OpenKeychain/src/main/res/xml/usb_device_filter.xml
@@ -32,6 +32,9 @@
     <usb-device class="11" vendor-id="8352" product-id="16648"/>
     <!-- Nitrokey Storage-->
     <usb-device class="11" vendor-id="8352" product-id="16649"/>
+
+    <!--GNUK based device are not supported right now-->
+    
     <!-- Nitrokey Start-->
     <!--<usb-device class="11" vendor-id="8352" product-id="16913"/>-->
     <!-- Default GNUK vid/pid-->