diff --git a/lib/class.js b/lib/class.js
index ae370b4..4996bf5 100644
--- a/lib/class.js
+++ b/lib/class.js
@@ -217,16 +217,10 @@ var extend = ( function( extending )
             members          = member_builder.initMembers(
                 prototype, prototype, prototype
             ),
-            abstract_methods = ( base.abstractMethods || [] ).slice();
 
-        // it's much faster to lookup a hash than it is to iterate through an
-        // entire array each time we need to find an existing abstract method
-        var abstract_map = {};
-        for ( var i = 0, len = abstract_methods.length; i < len; i++ )
-        {
-            var method = abstract_methods[ i ];
-            abstract_map[ method ] = i;
-        }
+            abstract_methods = util.clone( base.abstractMethods )
+                || { __length: 0 }
+        ;
 
         util.propParse( props, {
             each: function( name, value, keywords )
@@ -269,15 +263,17 @@ var extend = ( function( extending )
 
                 if ( is_abstract )
                 {
-                    abstract_methods.push( name );
+                    abstract_methods[ name ] = true;
+                    abstract_methods.__length++;
                 }
-                else if ( ( abstract_map[ name ] !== undefined )
+                else if ( ( abstract_methods[ name ] )
                     && ( is_abstract === false )
                 )
                 {
                     // if this was a concrete method, then it should no longer
                     // be marked as abstract
-                    delete abstract_methods[ abstract_map[ name ] ];
+                    delete abstract_methods[ name ];
+                    abstract_methods.__length--;
                 }
             },
 
@@ -289,8 +285,6 @@ var extend = ( function( extending )
             },
         } );
 
-        abstract_methods = util.arrayShrink( abstract_methods );
-
         // reference to the parent prototype (for more experienced users)
         prototype.parent = base.prototype;
 
@@ -332,7 +326,7 @@ var extend = ( function( extending )
     function createCtor( abstract_methods )
     {
         // concrete class
-        if ( abstract_methods.length === 0 )
+        if ( abstract_methods.__length === 0 )
         {
             var args = null;
 
@@ -507,7 +501,7 @@ function attachPropInit( prototype, properties )
  */
 function attachAbstract( func, methods )
 {
-    var is_abstract = ( methods.length > 0 ) ? true: false;
+    var is_abstract = ( methods.__length > 0 ) ? true: false;
 
     /**
      * Returns whether the class contains abstract methods (and is therefore
diff --git a/test/test-class-abstract.js b/test/test-class-abstract.js
index cbf3a1d..ab5883e 100644
--- a/test/test-class-abstract.js
+++ b/test/test-class-abstract.js
@@ -72,11 +72,6 @@ assert.ok(
     "All classes should have an isAbstract() method"
 );
 
-assert.ok(
-    ( Foo.abstractMethods instanceof Array ),
-    "All classes should provide a list of their abstract methods as an array"
-);
-
 assert.equal(
     Foo.isAbstract(),
     false,
@@ -96,28 +91,6 @@ assert.equal(
         "concrete implementation for all abstract methods"
 );
 
-assert.ok(
-    ( ( AbstractFoo.abstractMethods[ 0 ] == 'method' )
-        && ( AbstractFoo.abstractMethods[ 1 ] == 'second' )
-    ),
-    "Abstract classes should provide a list of their abstract methods' names"
-);
-
-assert.ok(
-    ( ( SubAbstractFoo.abstractMethods[ 0 ] == 'method' )
-        && ( SubAbstractFoo.abstractMethods[ 1 ] == undefined )
-    ),
-    "Abstract subclasses should not have their concrete methods within the " +
-        "the abstract method list if the concrete method was abstract in " +
-        "its supertype"
-);
-
-assert.equal(
-    ConcreteFoo.abstractMethods.length,
-    0,
-    "Concrete classes should not have any abstract methods listed"
-);
-
 assert.equal(
     ConcreteFoo.isAbstract(),
     false,
diff --git a/test/test-class-implement.js b/test/test-class-implement.js
index 3458794..cfb973a 100644
--- a/test/test-class-implement.js
+++ b/test/test-class-implement.js
@@ -112,6 +112,11 @@ var Type = Interface.extend( {
 } )();
 
 
+/**
+ * Since interfaces can contain only abstract methods, it stands to reason that
+ * any class implementing an interface without providing any concrete methods
+ * should be abstract by default.
+ */
 ( function testClassesImplementingInterfacesAreConsideredAbstractByDefault()
 {
     assert.equal(
@@ -123,40 +128,6 @@ var Type = Interface.extend( {
 } ) ();
 
 
-( function testAbstractMethodListUpdatedWhenInterfaceImplemented()
-{
-    // no base
-    assert.equal(
-        Foo.abstractMethods.length,
-        2,
-        "Abstract methods list is updated when interface is implemented " +
-            "(empty base)"
-    );
-
-    // PlainFoo base
-    assert.equal(
-        PlainFoo2.abstractMethods.length,
-        2,
-        "Abstract methods list is updated when interface is implemented " +
-            "(concrete base)"
-    );
-} )();
-
-
-( function testProperAbstractMethodsAreCopiedFromInterface()
-{
-    assert.ok(
-        ( ( Foo.abstractMethods[ 0 ] == 'foo' )
-            && ( Foo.abstractMethods[ 1 ] == 'foo2' )
-        )
-        && ( ( PlainFoo2.abstractMethods[ 0 ] == 'foo' )
-            && ( PlainFoo2.abstractMethods[ 1 ] == 'foo2' )
-        ),
-        "Abstract methods list contains names of implemented methods"
-    );
-} )();
-
-
 ( function testInstancesOfClassesAreInstancesOfTheirImplementedInterfaces()
 {
     // concrete implementation so that we can instantiate it
@@ -175,5 +146,11 @@ var Type = Interface.extend( {
         "Instances of classes implementing interfaces are considered to be " +
             "instances of the implemented interfaces"
     );
+
+    assert.equal(
+        ConcreteFoo.isAbstract(),
+        false,
+        "Concrete implementations are not considered to be abstract"
+    );
 } )();