diff --git a/lib/util.js b/lib/util.js
index f8049ad..23aaaca 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -228,7 +228,7 @@ exports.propCopy = function( props, dest, result_data )
                 }
                 else
                 {
-                    throw new Error(
+                    throw new TypeError(
                         "Cannot override property '" + name + "' with method"
                     );
                 }
@@ -339,7 +339,7 @@ function method_override(
             // that of its supertype
             if ( arg_len < super_method.definition.length )
             {
-                throw new Error(
+                throw new TypeError(
                     "Declaration of " + name + " must be compatiable " +
                         "with that of its supertype"
                 );
diff --git a/test/test-class-abstract.js b/test/test-class-abstract.js
index 98ebd59..732ec7f 100644
--- a/test/test-class-abstract.js
+++ b/test/test-class-abstract.js
@@ -172,14 +172,18 @@ assert.throws( function()
     });
 }, Error, "Concrete methods must implement the proper number of argments" );
 
-assert.throws( function()
-{
-    AbstractFoo.extend(
+assert.throws(
+    function()
     {
-        // incorrect number of arguments
-        method: abstractMethod(),
-    });
-}, Error, "Abstract methods of subtypes must implement the proper number of argments" );
+        AbstractFoo.extend(
+        {
+            // incorrect number of arguments
+            method: abstractMethod(),
+        });
+    },
+    TypeError,
+    "Abstract methods of subtypes must implement the proper number of argments"
+);
 
 assert.doesNotThrow(
     function()
@@ -205,7 +209,8 @@ assert.doesNotThrow(
             {
             },
         });
-    }, Error,
+    },
+    Error,
     "Concrete methods needn't implement the proper number of arguments if " +
         "no definition was provided"
 );
diff --git a/test/test-class-extend.js b/test/test-class-extend.js
index 7a84f75..49e99f0 100644
--- a/test/test-class-extend.js
+++ b/test/test-class-extend.js
@@ -133,5 +133,5 @@ assert.throws( function()
     {
         foo: function() {},
     });
-}, Error, "Cannot override property with a method" );
+}, TypeError, "Cannot override property with a method" );