diff --git a/pom.xml b/pom.xml
index ce2f133839..7b2820c28d 100644
--- a/pom.xml
+++ b/pom.xml
@@ -184,6 +184,11 @@
     <contributor>
       <name>Sam Yoon</name>
     </contributor>
+
+    <contributor>
+      <name>Hippo</name>
+      <email>hippah at protonmail.com</email>
+    </contributor>
   </contributors>
 
   <mailingLists>
diff --git a/src/main/java/org/apache/bcel/classfile/Attribute.java b/src/main/java/org/apache/bcel/classfile/Attribute.java
index 185360e60d..0b7b6bd8b8 100644
--- a/src/main/java/org/apache/bcel/classfile/Attribute.java
+++ b/src/main/java/org/apache/bcel/classfile/Attribute.java
@@ -93,6 +93,7 @@ protected static void println(final String msg) {
         }
     }
 
+
     /**
      * Class method reads one attribute from the input data stream. This method
      * must not be accessible from the outside. It is called by the Field and
@@ -110,6 +111,28 @@ protected static void println(final String msg) {
      */
     public static Attribute readAttribute(final DataInput file, final ConstantPool constant_pool)
             throws IOException, ClassFormatException
+    {
+        return readAttribute(file, constant_pool, false);
+    }
+
+    /**
+     * Class method reads one attribute from the input data stream. This method
+     * must not be accessible from the outside. It is called by the Field and
+     * Method constructor methods.
+     *
+     * @see Field
+     * @see Method
+     *
+     * @param file Input stream
+     * @param constant_pool Array of constants
+     * @param isOak If the the class file is oak
+     * @return Attribute
+     * @throws IOException
+     * @throws ClassFormatException
+     * @since 6.0
+     */
+    public static Attribute readAttribute(final DataInput file, final ConstantPool constant_pool, final boolean isOak)
+            throws IOException, ClassFormatException
     {
         byte tag = Const.ATTR_UNKNOWN; // Unknown attribute
         // Get class name from constant pool via `name_index' indirection
@@ -145,7 +168,7 @@ public static Attribute readAttribute(final DataInput file, final ConstantPool c
             case Const.ATTR_SOURCE_FILE:
                 return new SourceFile(name_index, length, file, constant_pool);
             case Const.ATTR_CODE:
-                return new Code(name_index, length, file, constant_pool);
+                return new Code(name_index, length, file, constant_pool, isOak);
             case Const.ATTR_EXCEPTIONS:
                 return new ExceptionTable(name_index, length, file, constant_pool);
             case Const.ATTR_LINE_NUMBER_TABLE:
diff --git a/src/main/java/org/apache/bcel/classfile/ClassParser.java b/src/main/java/org/apache/bcel/classfile/ClassParser.java
index a592bfed06..79a3b29174 100644
--- a/src/main/java/org/apache/bcel/classfile/ClassParser.java
+++ b/src/main/java/org/apache/bcel/classfile/ClassParser.java
@@ -58,6 +58,7 @@ public final class ClassParser {
     private Attribute[] attributes; // attributes defined in the class
     private final boolean isZip; // Loaded from zip file
     private static final int BUFSIZE = 8192;
+    private boolean isOak; // Is oak class file
 
 
     /**
@@ -290,7 +291,7 @@ private void readMethods() throws IOException, ClassFormatException {
         final int methods_count = dataInputStream.readUnsignedShort();
         methods = new Method[methods_count];
         for (int i = 0; i < methods_count; i++) {
-            methods[i] = new Method(dataInputStream, constantPool);
+            methods[i] = new Method(dataInputStream, constantPool, isOak);
         }
     }
 
@@ -303,5 +304,6 @@ private void readMethods() throws IOException, ClassFormatException {
     private void readVersion() throws IOException, ClassFormatException {
         minor = dataInputStream.readUnsignedShort();
         major = dataInputStream.readUnsignedShort();
+        isOak = major < Const.MAJOR_1_1 || (major == Const.MAJOR_1_1 && minor < 3);
     }
 }
diff --git a/src/main/java/org/apache/bcel/classfile/Code.java b/src/main/java/org/apache/bcel/classfile/Code.java
index cedc53527e..6a1e06b8a2 100644
--- a/src/main/java/org/apache/bcel/classfile/Code.java
+++ b/src/main/java/org/apache/bcel/classfile/Code.java
@@ -48,6 +48,7 @@ public final class Code extends Attribute {
     private byte[] code; // Actual byte code
     private CodeException[] exceptionTable; // Table of handled exceptions
     private Attribute[] attributes; // or LocalVariable
+    private boolean isOak; // If the class file follows oak format
 
 
     /**
@@ -60,6 +61,7 @@ public Code(final Code c) {
     }
 
 
+
     /**
      * @param name_index Index pointing to the name <em>Code</em>
      * @param length Content length in bytes
@@ -68,10 +70,23 @@ public Code(final Code c) {
      */
     Code(final int name_index, final int length, final DataInput file, final ConstantPool constant_pool)
             throws IOException {
+        this(name_index, length, file, constant_pool, false);
+    }
+
+    /**
+     * @param name_index Index pointing to the name <em>Code</em>
+     * @param length Content length in bytes
+     * @param file Input stream
+     * @param constant_pool Array of constants
+     * @param isOak If the class file is oak
+     */
+    Code(final int name_index, final int length, final DataInput file, final ConstantPool constant_pool, final boolean isOak)
+            throws IOException {
         // Initialize with some default values which will be overwritten later
-        this(name_index, length, file.readUnsignedShort(), file.readUnsignedShort(), (byte[]) null,
-                (CodeException[]) null, (Attribute[]) null, constant_pool);
-        final int code_length = file.readInt();
+        this(name_index, length, isOak ? file.readUnsignedByte() : file.readUnsignedShort(), isOak ? file.readUnsignedByte() : file.readUnsignedShort(),
+                (byte[]) null, (CodeException[]) null, (Attribute[]) null, constant_pool);
+        this.isOak = isOak;
+        final int code_length = isOak ? file.readUnsignedShort() : file.readInt();
         code = new byte[code_length]; // Read byte code
         file.readFully(code);
         /* Read exception table that contains all regions where an exception
@@ -109,13 +124,30 @@ public Code(final Code c) {
      * @param constant_pool Array of constants
      */
     public Code(final int name_index, final int length, final int maxStack, final int maxLocals, final byte[] code,
-            final CodeException[] exceptionTable, final Attribute[] attributes, final ConstantPool constant_pool) {
+                final CodeException[] exceptionTable, final Attribute[] attributes, final ConstantPool constant_pool) {
+        this(name_index, length, maxStack, maxLocals, code, exceptionTable, attributes, constant_pool, false);
+    }
+
+    /**
+     * @param name_index Index pointing to the name <em>Code</em>
+     * @param length Content length in bytes
+     * @param maxStack Maximum size of stack
+     * @param maxLocals Number of local variables
+     * @param code Actual byte code
+     * @param exceptionTable of handled exceptions
+     * @param attributes Attributes of code: LineNumber or LocalVariable
+     * @param constant_pool Array of constants
+     * @param isOak If the class file follows the oak format
+     */
+    public Code(final int name_index, final int length, final int maxStack, final int maxLocals, final byte[] code,
+            final CodeException[] exceptionTable, final Attribute[] attributes, final ConstantPool constant_pool, final boolean isOak) {
         super(Const.ATTR_CODE, name_index, length, constant_pool);
         this.maxStack = maxStack;
         this.maxLocals = maxLocals;
         this.code = code != null ? code : ArrayUtils.EMPTY_BYTE_ARRAY;
         this.exceptionTable = exceptionTable != null ? exceptionTable : CodeException.EMPTY_CODE_EXCEPTION_ARRAY;
         this.attributes = attributes != null ? attributes : EMPTY_ATTRIBUTE_ARRAY;
+        this.isOak = isOak;
         super.setLength(calculateLength()); // Adjust length
     }
 
@@ -142,9 +174,15 @@ public void accept( final Visitor v ) {
     @Override
     public void dump( final DataOutputStream file ) throws IOException {
         super.dump(file);
-        file.writeShort(maxStack);
-        file.writeShort(maxLocals);
-        file.writeInt(code.length);
+        if (isOak) {
+            file.writeByte(maxStack);
+            file.writeByte(maxLocals);
+            file.writeShort(code.length);
+        } else {
+            file.writeShort(maxStack);
+            file.writeShort(maxLocals);
+            file.writeInt(code.length);
+        }
         file.write(code, 0, code.length);
         file.writeShort(exceptionTable.length);
         for (final CodeException exception : exceptionTable) {
@@ -230,7 +268,19 @@ public int getMaxStack() {
      * and excluding all its attributes
      */
     private int getInternalLength() {
-        return 2 /*maxStack*/+ 2 /*maxLocals*/+ 4 /*code length*/
+        final int maxStack;
+        final int maxLocals;
+        final int codeLength;
+        if (isOak) {
+            maxStack = 1;
+            maxLocals = 1;
+            codeLength = 2;
+        } else {
+            maxStack = 2;
+            maxLocals = 2;
+            codeLength = 4;
+        }
+        return maxStack + maxLocals + codeLength
                 + code.length /*byte-code*/
                 + 2 /*exception-table length*/
                 + 8 * (exceptionTable == null ? 0 : exceptionTable.length) /* exception table */
diff --git a/src/main/java/org/apache/bcel/classfile/FieldOrMethod.java b/src/main/java/org/apache/bcel/classfile/FieldOrMethod.java
index 6b70942185..8ed8e82d67 100644
--- a/src/main/java/org/apache/bcel/classfile/FieldOrMethod.java
+++ b/src/main/java/org/apache/bcel/classfile/FieldOrMethod.java
@@ -100,12 +100,23 @@ protected FieldOrMethod(final DataInputStream file, final ConstantPool constant_
      * @throws ClassFormatException
      */
     protected FieldOrMethod(final DataInput file, final ConstantPool constant_pool) throws IOException, ClassFormatException {
+        this(file, constant_pool, false);
+    }
+
+    /**
+     * Construct object from file stream.
+     * @param file Input stream
+     * @param isOak If the class file is oak
+     * @throws IOException
+     * @throws ClassFormatException
+     */
+    protected FieldOrMethod(final DataInput file, final ConstantPool constant_pool, final boolean isOak) throws IOException, ClassFormatException {
         this(file.readUnsignedShort(), file.readUnsignedShort(), file.readUnsignedShort(), null,
                 constant_pool);
         final int attributes_count = file.readUnsignedShort();
         attributes = new Attribute[attributes_count];
         for (int i = 0; i < attributes_count; i++) {
-            attributes[i] = Attribute.readAttribute(file, constant_pool);
+            attributes[i] = Attribute.readAttribute(file, constant_pool, isOak);
         }
         this.attributes_count = attributes_count; // init deprecated field
     }
diff --git a/src/main/java/org/apache/bcel/classfile/Method.java b/src/main/java/org/apache/bcel/classfile/Method.java
index a414de7a49..ebbe539753 100644
--- a/src/main/java/org/apache/bcel/classfile/Method.java
+++ b/src/main/java/org/apache/bcel/classfile/Method.java
@@ -84,7 +84,19 @@ public Method(final Method c) {
      */
     Method(final DataInput file, final ConstantPool constant_pool) throws IOException,
             ClassFormatException {
-        super(file, constant_pool);
+        this(file, constant_pool, false);
+    }
+
+    /**
+     * Construct object from file stream.
+     * @param file Input stream
+     * @param isOak If the class file is oak
+     * @throws IOException
+     * @throws ClassFormatException
+     */
+    Method(final DataInput file, final ConstantPool constant_pool, final boolean isOak) throws IOException,
+            ClassFormatException {
+        super(file, constant_pool, isOak);
     }