diff --git a/android/src/com/google/zxing/client/android/DecodeHandler.java b/android/src/com/google/zxing/client/android/DecodeHandler.java
index 9a43ed849..e477baf01 100644
--- a/android/src/com/google/zxing/client/android/DecodeHandler.java
+++ b/android/src/com/google/zxing/client/android/DecodeHandler.java
@@ -38,6 +38,7 @@ final class DecodeHandler extends Handler {
 
   private final CaptureActivity activity;
   private final MultiFormatReader multiFormatReader;
+  private boolean running = true;
 
   DecodeHandler(CaptureActivity activity, Hashtable<DecodeHintType, Object> hints) {
     multiFormatReader = new MultiFormatReader();
@@ -47,11 +48,15 @@ final class DecodeHandler extends Handler {
 
   @Override
   public void handleMessage(Message message) {
+    if (!running) {
+      return;
+    }
     switch (message.what) {
       case R.id.decode:
         decode((byte[]) message.obj, message.arg1, message.arg2);
         break;
       case R.id.quit:
+        running = false;
         Looper.myLooper().quit();
         break;
     }
diff --git a/core/src/com/google/zxing/datamatrix/decoder/DecodedBitStreamParser.java b/core/src/com/google/zxing/datamatrix/decoder/DecodedBitStreamParser.java
index 9343b386d..93964220d 100644
--- a/core/src/com/google/zxing/datamatrix/decoder/DecodedBitStreamParser.java
+++ b/core/src/com/google/zxing/datamatrix/decoder/DecodedBitStreamParser.java
@@ -43,12 +43,12 @@ final class DecodedBitStreamParser {
     'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N',
     'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'
   };
-  
+
   private static final char[] C40_SHIFT2_SET_CHARS = {
     '!', '"', '#', '$', '%', '&', '\'', '(', ')', '*',  '+', ',', '-', '.',
     '/', ':', ';', '<', '=', '>', '?',  '@', '[', '\\', ']', '^', '_'
   };
-  
+
   /**
    * See ISO 16022:2006, Annex C Table C.2
    * The Text Basic Character Set (*'s used for placeholders for the shift values)
@@ -58,12 +58,12 @@ final class DecodedBitStreamParser {
     'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
     'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'
   };
-  
+
   private static final char[] TEXT_SHIFT3_SET_CHARS = {
     '\'', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N',
     'O',  'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '{', '|', '}', '~', (char) 127
   };
-  
+
   private static final int PAD_ENCODE = 0;  // Not really an encoding
   private static final int ASCII_ENCODE = 1;
   private static final int C40_ENCODE = 2;
@@ -112,7 +112,7 @@ final class DecodedBitStreamParser {
     }
     return new DecoderResult(bytes, result.toString(), byteSegments.isEmpty() ? null : byteSegments, null);
   }
-  
+
   /**
    * See ISO 16022:2006, 5.2.3 and Annex C, Table C.2
    */
@@ -257,7 +257,7 @@ final class DecodedBitStreamParser {
       }
     } while (bits.available() > 0);
   }
-  
+
   /**
    * See ISO 16022:2006, 5.2.6 and Annex C, Table C.2
    */
@@ -347,7 +347,7 @@ final class DecodedBitStreamParser {
       }
     } while (bits.available() > 0);
   }
-  
+
   /**
    * See ISO 16022:2006, 5.2.7
    */
@@ -398,7 +398,7 @@ final class DecodedBitStreamParser {
     result[1] = temp;
     result[2] = fullBitValue - temp * 40;
   }
-  
+
   /**
    * See ISO 16022:2006, 5.2.8 and Annex C Table C.3
    */
@@ -419,7 +419,7 @@ final class DecodedBitStreamParser {
           // If we encounter the unlatch code then continue reading because the Codeword triple
           // is padded with 0's
         }
-        
+
         if (!unlatch) {
           if ((edifactValue & 32) == 0) {  // no 1 in the leading (6th) bit
             edifactValue |= 64;  // Add a leading 01 to the 6 bit binary value
@@ -429,7 +429,7 @@ final class DecodedBitStreamParser {
       }
     } while (!unlatch && bits.available() > 0);
   }
-  
+
   /**
    * See ISO 16022:2006, 5.2.9 and Annex B, B.2
    */
@@ -446,6 +446,12 @@ final class DecodedBitStreamParser {
     } else {
       count = 250 * (d1 - 249) + unrandomize255State(bits.readBits(8), codewordPosition++);
     }
+
+    // We're seeing NegativeArraySizeException errors from users.
+    if (count < 0) {
+      throw FormatException.getFormatInstance();
+    }
+
     byte[] bytes = new byte[count];
     for (int i = 0; i < count; i++) {
       // Have seen this particular error in the wild, such as at
@@ -462,7 +468,7 @@ final class DecodedBitStreamParser {
       throw new RuntimeException("Platform does not support required encoding: " + uee);
     }
   }
-  
+
   /**
    * See ISO 16022:2006, Annex B, B.2
    */
@@ -472,5 +478,5 @@ final class DecodedBitStreamParser {
     int tempVariable = randomizedBase256Codeword - pseudoRandomNumber;
     return (byte) (tempVariable >= 0 ? tempVariable : tempVariable + 256);
   }
-  
+
 }
diff --git a/core/src/com/google/zxing/qrcode/decoder/DecodedBitStreamParser.java b/core/src/com/google/zxing/qrcode/decoder/DecodedBitStreamParser.java
index 085c4d5bc..ff374ac50 100644
--- a/core/src/com/google/zxing/qrcode/decoder/DecodedBitStreamParser.java
+++ b/core/src/com/google/zxing/qrcode/decoder/DecodedBitStreamParser.java
@@ -126,6 +126,11 @@ final class DecodedBitStreamParser {
   private static void decodeHanziSegment(BitSource bits,
                                          StringBuffer result,
                                          int count) throws FormatException {
+    // Don't crash trying to read more bits than we have available.
+    if (count * 13 > bits.available()) {
+      throw FormatException.getFormatInstance();
+    }
+
     // Each character will require 2 bytes. Read the characters as 2-byte pairs
     // and decode as GB2312 afterwards
     byte[] buffer = new byte[2 * count];
@@ -146,7 +151,7 @@ final class DecodedBitStreamParser {
       offset += 2;
       count--;
     }
-    
+
     try {
       result.append(new String(buffer, StringUtils.GB2312));
     } catch (UnsupportedEncodingException uee) {
@@ -157,6 +162,11 @@ final class DecodedBitStreamParser {
   private static void decodeKanjiSegment(BitSource bits,
                                          StringBuffer result,
                                          int count) throws FormatException {
+    // Don't crash trying to read more bits than we have available.
+    if (count * 13 > bits.available()) {
+      throw FormatException.getFormatInstance();
+    }
+
     // Each character will require 2 bytes. Read the characters as 2-byte pairs
     // and decode as Shift_JIS afterwards
     byte[] buffer = new byte[2 * count];
@@ -191,10 +201,12 @@ final class DecodedBitStreamParser {
                                         CharacterSetECI currentCharacterSetECI,
                                         Vector byteSegments,
                                         Hashtable hints) throws FormatException {
-    byte[] readBytes = new byte[count];
+    // Don't crash trying to read more bits than we have available.
     if (count << 3 > bits.available()) {
       throw FormatException.getFormatInstance();
     }
+
+    byte[] readBytes = new byte[count];
     for (int i = 0; i < count; i++) {
       readBytes[i] = (byte) bits.readBits(8);
     }
@@ -289,7 +301,7 @@ final class DecodedBitStreamParser {
       result.append(toAlphaNumericChar(digitBits));
     }
   }
-  
+
   private static int parseECIValue(BitSource bits) {
     int firstByte = bits.readBits(8);
     if ((firstByte & 0x80) == 0) {
diff --git a/core/src/com/google/zxing/qrcode/detector/Detector.java b/core/src/com/google/zxing/qrcode/detector/Detector.java
index f5bd96351..724d39d59 100644
--- a/core/src/com/google/zxing/qrcode/detector/Detector.java
+++ b/core/src/com/google/zxing/qrcode/detector/Detector.java
@@ -308,14 +308,19 @@ public class Detector {
     int dx = Math.abs(toX - fromX);
     int dy = Math.abs(toY - fromY);
     int error = -dx >> 1;
-    int ystep = fromY < toY ? 1 : -1;
     int xstep = fromX < toX ? 1 : -1;
-    int state = 0; // In black pixels, looking for white, first or second time
-    for (int x = fromX, y = fromY; x != toX; x += xstep) {
+    int ystep = fromY < toY ? 1 : -1;
 
+    // In black pixels, looking for white, first or second time.
+    int state = 0;
+    for (int x = fromX, y = fromY; x != toX; x += xstep) {
       int realX = steep ? y : x;
       int realY = steep ? x : y;
-      if (state == 1) { // In white pixels, looking for black
+
+      // In white pixels, looking for black.
+      // FIXME(dswitkin): This method seems to assume square images, which can cause these calls to
+      // BitMatrix.get() to throw ArrayIndexOutOfBoundsException.
+      if (state == 1) {
         if (image.get(realX, realY)) {
           state++;
         }
@@ -325,7 +330,8 @@ public class Detector {
         }
       }
 
-      if (state == 3) { // Found black, white, black, and stumbled back onto white; done
+      // Found black, white, black, and stumbled back onto white, so we're done.
+      if (state == 3) {
         int diffX = x - fromX;
         int diffY = y - fromY;
         if (xstep < 0) {