diff --git a/src/zutil/ByteUtil.java b/src/zutil/ByteUtil.java
index aad21cf..c934eef 100755
--- a/src/zutil/ByteUtil.java
+++ b/src/zutil/ByteUtil.java
@@ -64,7 +64,7 @@ public class ByteUtil {
      * @return a new byte containing a sub byte defined by the index and length
      */
     public static byte getBits(byte data, int length){
-        return getBits(data, 0, length);
+        return getBits(data, length-1, length);
     }
 
     /**
@@ -119,9 +119,9 @@ public class ByteUtil {
     public static byte getBitMask(int index, int length) {
         --length;
         if(0 > index || index > 7)
-            throw new IllegalArgumentException("Invalid index argument, allowed value is 0-7");
-        if(length < 0 || 7-index-length < 0)
-            throw new IllegalArgumentException("Invalid length argument: "+length+", allowed values 1-8 depending on index");
+            throw new IllegalArgumentException("Invalid index argument, allowed values: 0-7");
+        if(length < 0 || index-length < 0)
+            throw new IllegalArgumentException("Invalid length argument: "+length+", allowed values: 1 to "+(index+1)+" for index "+index);
         return (byte) BYTE_MASK[index][length];
     }
 }
diff --git a/test/zutil/ByteUtilTest.java b/test/zutil/ByteUtilTest.java
index 2000d28..2c28fad 100755
--- a/test/zutil/ByteUtilTest.java
+++ b/test/zutil/ByteUtilTest.java
@@ -48,6 +48,14 @@ public class ByteUtilTest {
     }
 
 
+    @Test
+    public void getBits(){
+        assertEquals(0x01, ByteUtil.getBits((byte)0xFF, 1));
+        assertEquals(0x0F, ByteUtil.getBits((byte)0xFF, 4));
+        assertEquals((byte)0xFF, ByteUtil.getBits((byte)0xFF, 8));
+
+    }
+
     @Test
     public void getBitsArray(){
         assertArrayEquals(new byte[]{}, ByteUtil.getBits(new byte[]{0x00}, 0));