diff --git a/lib/member_builder.js b/lib/member_builder.js
index 559e6bc..f47cb4c 100644
--- a/lib/member_builder.js
+++ b/lib/member_builder.js
@@ -74,8 +74,51 @@ exports.buildMethod = function(
 {
     // TODO: We can improve performance by not scanning each one individually
     // every time this method is called
-    var prev_data     = scanMembers( members, name, base ),
-        prev          = ( prev_data ) ? prev_data.member : null,
+    var prev_data = scanMembers( members, name, base ),
+        prev      = ( prev_data ) ? prev_data.member : null,
+        dest      = getMemberVisibility( members, keywords );
+    ;
+
+    // ensure that the declaration is valid (keywords make sense, argument
+    // length, etc)
+    validateMethod( keywords, prev_data, value, name );
+
+    // we might be overriding an existing method
+    if ( prev )
+    {
+        // override the method
+        dest[ name ] = overrideMethod( prev, value, instCallback, cid );
+    }
+    else if ( keywords[ 'abstract' ] )
+    {
+        // we do not want to wrap abstract methods, since they are not callable
+        dest[ name ] = value;
+    }
+    else
+    {
+        // we are not overriding the method, so simply copy it over, wrapping it
+        // to ensure privileged calls will work properly
+        dest[ name ] = overrideMethod( value, null, instCallback, cid );
+    }
+
+    // store keywords for later reference (needed for pre-ES5 fallback)
+    dest[ name ].___$$keywords$$ = keywords;
+};
+
+
+/**
+ * Validates a method declaration, ensuring that keywords are valid, overrides
+ * make sense, etc.
+ *
+ * @param  {Object.<string,boolean>}  keywords  parsed keywords
+ *
+ * @param  {Object}  prev_data  data of member being overridden, if available
+ * @param  {*}       value      property value
+ * @param  {string}  name       property name
+ */
+function validateMethod( keywords, prev_data, value, name )
+{
+    var prev          = ( prev_data ) ? prev_data.member : null,
         prev_keywords = ( prev && prev.___$$keywords$$ )
             ? prev.___$$keywords$$
             : {}
@@ -155,30 +198,7 @@ exports.buildMethod = function(
             );
         }
     }
-
-    var dest = getMemberVisibility( members, keywords );
-
-    // we might be overriding an existing method
-    if ( prev )
-    {
-        // override the method
-        dest[ name ] = overrideMethod( prev, value, instCallback, cid );
-    }
-    else if ( keywords[ 'abstract' ] )
-    {
-        // we do not want to wrap abstract methods, since they are not callable
-        dest[ name ] = value;
-    }
-    else
-    {
-        // we are not overriding the method, so simply copy it over, wrapping it
-        // to ensure privileged calls will work properly
-        dest[ name ] = overrideMethod( value, null, instCallback, cid );
-    }
-
-    // store keywords for later reference (needed for pre-ES5 fallback)
-    dest[ name ].___$$keywords$$ = keywords;
-};
+}
 
 
 /**