diff --git a/Mifare Classic Tool/app/src/main/java/de/syss/MifareClassicTool/Activities/KeyMapCreator.java b/Mifare Classic Tool/app/src/main/java/de/syss/MifareClassicTool/Activities/KeyMapCreator.java
index ffa3272d..45ff7621 100644
--- a/Mifare Classic Tool/app/src/main/java/de/syss/MifareClassicTool/Activities/KeyMapCreator.java	
+++ b/Mifare Classic Tool/app/src/main/java/de/syss/MifareClassicTool/Activities/KeyMapCreator.java	
@@ -142,6 +142,7 @@ public class KeyMapCreator extends BasicActivity {
     private File mKeyDirPath;
     private int mFirstSector;
     private int mLastSector;
+    private MCReader currentReader;
 
     /**
      * Set layout, set the mapping range
@@ -331,6 +332,9 @@ private void selectKeyFiles(boolean allOrNone) {
     public void onCancelCreateKeyMap(View view) {
         if (mIsCreatingKeyMap) {
             mIsCreatingKeyMap = false;
+            if (currentReader != null) {
+                currentReader.cancelCreateKeyMap();
+            }
             mCancel.setEnabled(false);
         } else {
             finish();
@@ -395,6 +399,7 @@ public void onCreateKeyMap(View view) {
 
                 // Create reader.
                 MCReader reader = Common.checkForTagAndCreateReader(this);
+                currentReader = reader;
                 if (reader == null) {
                     return;
                 }
diff --git a/Mifare Classic Tool/app/src/main/java/de/syss/MifareClassicTool/MCReader.java b/Mifare Classic Tool/app/src/main/java/de/syss/MifareClassicTool/MCReader.java
index df8ab708..5adf94cc 100644
--- a/Mifare Classic Tool/app/src/main/java/de/syss/MifareClassicTool/MCReader.java	
+++ b/Mifare Classic Tool/app/src/main/java/de/syss/MifareClassicTool/MCReader.java	
@@ -65,6 +65,7 @@ public class MCReader {
     private int mFirstSector = 0;
     private ArrayList<String> mKeysWithOrder;
     private boolean mHasAllZeroKey = false;
+    private boolean cancelCreateKeyMap = false;
 
     /**
      * Initialize a MIFARE Classic reader for the given tag.
@@ -107,6 +108,10 @@ public static MCReader get(Tag tag) {
         return mcr;
     }
 
+    public void cancelCreateKeyMap() {
+        cancelCreateKeyMap = true;
+    }
+
     /**
      * Read as much as possible from the tag with the given key information.
      * @param keyMap Keys (A and B) mapped to a sector.
@@ -460,6 +465,7 @@ public int writeValueBlock(int sectorIndex, int blockIndex, int value,
     public int buildNextKeyMapPart() {
         // Clear status and key map before new walk through sectors.
         boolean error = false;
+        cancelCreateKeyMap = false;
         if (mKeysWithOrder != null && mLastSector != -1) {
             if (mKeyMapStatus == mLastSector+1) {
                 mKeyMapStatus = mFirstSector;
@@ -487,6 +493,9 @@ public int buildNextKeyMapPart() {
                 byte[] bytesKey = Common.hex2Bytes(key);
                 for (int j = 0; j < retryAuthCount+1;) {
                     try {
+                        if (cancelCreateKeyMap) {
+                            return -1;
+                        }
                         if (!foundKeys[0]) {
                             auth = mMFC.authenticateSectorWithKeyA(
                                     mKeyMapStatus, bytesKey);