diff --git a/Foundation/CPSet.j b/Foundation/CPSet.j
index 1d40c7987..7026a376e 100644
--- a/Foundation/CPSet.j
+++ b/Foundation/CPSet.j
@@ -232,7 +232,9 @@
 */
 - (BOOL)containsObject:(id)anObject
 {
-    if (_contents[[anObject UID]] && [_contents[[anObject UID]] isEqual:anObject])
+    var obj = _contents[[anObject UID]];
+
+    if (obj !== undefined && [obj isEqual:anObject])
         return YES;
     
     return NO;
diff --git a/Tests/Foundation/CPSetTest.j b/Tests/Foundation/CPSetTest.j
new file mode 100644
index 000000000..905d8fdb8
--- /dev/null
+++ b/Tests/Foundation/CPSetTest.j
@@ -0,0 +1,59 @@
+
+@import <Foundation/CPSet.j>
+
+@implementation CPSetTest : OJTestCase
+{
+    CPSet set;
+}
+
+- (void)setUp
+{
+    set = [CPSet new];
+}
+
+- (void)testAddObject
+{
+    [self assertFalse:[set containsObject:"foo"]];
+    [set addObject:"foo"];
+    [self assertTrue:[set containsObject:"foo"]];
+}
+
+- (void)testAddZeroObject
+{
+    [self assertFalse:[set containsObject:0]];
+    [set addObject:0];
+    [self assertTrue:[set containsObject:0]];
+}
+
+- (void)testRemoveObject
+{
+    [set addObject:"foo"];
+    [self assertTrue:[set containsObject:"foo"]];
+    [set removeObject:"foo"];
+    [self assertFalse:[set containsObject:"foo"]];
+}
+
+- (void)testRemoveZeroObject
+{
+    [set addObject:0];
+    [self assertTrue:[set containsObject:0]];
+    [set removeObject:0];
+    [self assertFalse:[set containsObject:0]];
+}
+
+- (void)testAddNilObject
+{
+    [self assertFalse:[set containsObject:nil]];
+    [set addObject:nil];
+    [self assertFalse:[set containsObject:nil]];
+}
+
+- (void)testRemoveNilObject
+{
+    [set addObject:nil];
+    [self assertFalse:[set containsObject:nil]];
+    [set removeObject:nil];
+    [self assertFalse:[set containsObject:nil]];
+}
+
+@end