diff --git a/Foundation/CPArray/CPMutableArray.j b/Foundation/CPArray/CPMutableArray.j
index e9588dd51..94eecdb00 100644
--- a/Foundation/CPArray/CPMutableArray.j
+++ b/Foundation/CPArray/CPMutableArray.j
@@ -397,6 +397,17 @@
 
 @end
 
+@implementation CPArray (CPMutableCopying)
+
+- (id)mutableCopy
+{
+    var r = [CPMutableArray new];
+    [r addObjectsFromArray:self];
+    return r;
+}
+
+@end
+
 var selectorCompare = function selectorCompare(object1, object2, selector)
 {
     return [object1 performSelector:selector withObject:object2];
diff --git a/Tests/Foundation/CPMutableArrayTest.j b/Tests/Foundation/CPMutableArrayTest.j
index 44fcba9f6..8cb356633 100644
--- a/Tests/Foundation/CPMutableArrayTest.j
+++ b/Tests/Foundation/CPMutableArrayTest.j
@@ -2,7 +2,6 @@
 @import <Foundation/Foundation.j>
 @import "CPArrayTest.j"
 
-
 @implementation CPMutableArrayTest : CPArrayTest
 
 + (Class)arrayClass
@@ -448,6 +447,19 @@
     [self assert:[5, 4, 4, 3, 2, 2, 1, 1, 1, 1] equals:target];
 }
 
+- (void)testMutableCopy
+{
+    var normalArray = [CPArray array];
+
+    [self assertThrows:function () { [array addObject:[CPNull null]] }];
+
+    var mutableArray = [normalArray mutableCopy];
+
+    [mutableArray addObject:[CPNull null]];
+
+    [self assert:1 equals:[mutableArray count] message:"mutable copy should have content"];
+}
+
 @end
 
 @implementation CPPrettyObject : CPObject