diff --git a/Headers/Foundation/NSOrderedSet.h b/Headers/Foundation/NSOrderedSet.h
index 0d17bcc3d..39fe0ef65 100644
--- a/Headers/Foundation/NSOrderedSet.h
+++ b/Headers/Foundation/NSOrderedSet.h
@@ -67,12 +67,12 @@ extern "C" {
                          copyItems:(BOOL)flag;
 
 // instance methods
-- (instancetype) initWithArray:(GS_GENERIC_CLASS(NSArray, ElementT)*)other;
-- (instancetype) initWithArray:(GS_GENERIC_CLASS(NSArray, ElementT)*)other copyItems:(BOOL)flag;
-- (instancetype) initWithArray:(GS_GENERIC_CLASS(NSArray, ElementT)*)other
+- (instancetype) initWithArray:(GS_GENERIC_CLASS(NSArray, ElementT)*)array;
+- (instancetype) initWithArray:(GS_GENERIC_CLASS(NSArray, ElementT)*)array copyItems:(BOOL)flag;
+- (instancetype) initWithArray:(GS_GENERIC_CLASS(NSArray, ElementT)*)array
                          range:(NSRange)range
                      copyItems:(BOOL)flag;
-  - (instancetype) initWithObject:(id)object;
+- (instancetype) initWithObject:(id)object;
 - (instancetype) initWithObjects:(GS_GENERIC_TYPE(ElementT))firstObject, ...;
 - (instancetype) initWithObjects:(const GS_GENERIC_TYPE(ElementT)[])objects
                            count:(NSUInteger)count;
@@ -119,7 +119,7 @@ extern "C" {
                             passingTest:(GSPredicateBlock)predicate;
 - (GS_GENERIC_CLASS(NSEnumerator, ElementT)*) objectEnumerator;
 - (GS_GENERIC_CLASS(NSEnumerator, ElementT)*) reverseObjectEnumerator;
-  - (NSOrderedSet *)reversedOrderedSet;
+- (NSOrderedSet *)reversedOrderedSet;
 - (void) getObjects: (__unsafe_unretained GS_GENERIC_TYPE(ElementT)[])aBuffer
               range: (NSRange)aRange;
 
diff --git a/Source/GSOrderedSet.m b/Source/GSOrderedSet.m
new file mode 100644
index 000000000..2c883e5b0
--- /dev/null
+++ b/Source/GSOrderedSet.m
@@ -0,0 +1,837 @@
+/** Concrete implementation of NSSet based on GNU Set class
+   Copyright (C) 2019 Free Software Foundation, Inc.
+
+   Written by: Gregory Casamento <greg.casamento@gmail.com>
+   Created: May 17 2019
+
+   This file is part of the GNUstep Base Library.
+
+   This library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   _version 2 of the License, or (at your option) any later _version.
+
+   This library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Library General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with this library; if not, write to the Free
+   Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+   Boston, MA 02111 USA.
+   */
+
+#import "common.h"
+#import "Foundation/NSSet.h"
+#import "GNUstepBase/GSObjCRuntime.h"
+#import "Foundation/NSAutoreleasePool.h"
+#import "Foundation/NSArray.h"
+#import "Foundation/NSEnumerator.h"
+#import "Foundation/NSException.h"
+#import "Foundation/NSPortCoder.h"
+// For private method _decodeArrayOfObjectsForKey:
+#import "Foundation/NSKeyedArchiver.h"
+#import "GSPrivate.h"
+
+#define	GSI_MAP_HAS_VALUE	0
+#define	GSI_MAP_KTYPES		GSUNION_OBJ
+
+
+#include "GNUstepBase/GSIMap.h"
+
+static SEL	memberSel;
+static SEL      privateCountOfSel;
+@interface GSOrderedSet : NSOrderedSet
+{
+@public
+  GSIMapTable_t	map;
+}
+@end
+
+@interface GSMutableSet : NSMutableSet
+{
+@public
+  GSIMapTable_t	map;
+@private
+  NSUInteger _version;
+}
+@end
+
+@interface GSSetEnumerator : NSEnumerator
+{
+  GSSet			*set;
+  GSIMapEnumerator_t	enumerator;
+}
+@end
+
+@implementation GSSetEnumerator
+
+- (id) initWithSet: (NSSet*)d
+{
+  self = [super init];
+  if (self != nil)
+    {
+      set = (GSSet*)RETAIN(d);
+      enumerator = GSIMapEnumeratorForMap(&set->map);
+    }
+  return self;
+}
+
+- (id) nextObject
+{
+  GSIMapNode node = GSIMapEnumeratorNextNode(&enumerator);
+
+  if (node == 0)
+    {
+      return nil;
+    }
+  return node->key.obj;
+}
+
+- (void) dealloc
+{
+  GSIMapEndEnumerator(&enumerator);
+  RELEASE(set);
+  [super dealloc];
+}
+
+@end
+
+
+@implementation GSSet
+
+static Class	arrayClass;
+static Class	setClass;
+static Class	mutableSetClass;
+
++ (void) initialize
+{
+  if (self == [GSSet class])
+    {
+      arrayClass = [NSArray class];
+      setClass = [GSSet class];
+      mutableSetClass = [GSMutableSet class];
+      memberSel = @selector(member:);
+      privateCountOfSel = @selector(_countForObject:);
+    }
+}
+
+- (NSArray*) allObjects
+{
+  GSIMapEnumerator_t	enumerator = GSIMapEnumeratorForMap(&map);
+  GSIMapNode 		node = GSIMapEnumeratorNextNode(&enumerator);
+  NSUInteger		i = 0;
+  NSArray		*result;
+  GS_BEGINIDBUF(objects, map.nodeCount);
+
+  while (node != 0)
+    {
+      objects[i++] = node->key.obj;
+      node = GSIMapEnumeratorNextNode(&enumerator);
+    }
+  GSIMapEndEnumerator(&enumerator);
+  result = AUTORELEASE([[arrayClass allocWithZone: NSDefaultMallocZone()]
+    initWithObjects: objects count: i]);
+  GS_ENDIDBUF();
+  return result;
+}
+
+- (id) anyObject
+{
+  if (map.nodeCount > 0)
+    {
+      GSIMapBucket bucket = map.buckets;
+
+      while (1)
+	{
+	  if (bucket->firstNode)
+	    {
+	      return bucket->firstNode->key.obj;
+	    }
+	  else
+	    {
+	      bucket++;
+	    }
+	}
+    }
+  else
+    {
+      return nil;
+    }
+}
+
+- (id) copyWithZone: (NSZone*)z
+{
+  return RETAIN(self);
+}
+
+- (NSUInteger) count
+{
+  return map.nodeCount;
+}
+
+- (void) dealloc
+{
+  GSIMapEmptyMap(&map);
+  [super dealloc];
+}
+
+- (void) encodeWithCoder: (NSCoder*)aCoder
+{
+  if ([aCoder allowsKeyedCoding])
+    {
+      [super encodeWithCoder: aCoder];
+    }
+  else
+    {
+      unsigned		count = map.nodeCount;
+      SEL			sel = @selector(encodeObject:);
+      IMP			imp = [aCoder methodForSelector: sel];
+      GSIMapEnumerator_t	enumerator = GSIMapEnumeratorForMap(&map);
+      GSIMapNode 		node = GSIMapEnumeratorNextNode(&enumerator);
+
+      [aCoder encodeValueOfObjCType: @encode(unsigned) at: &count];
+      while (node != 0)
+	{
+	  (*imp)(aCoder, sel, node->key.obj);
+	  node = GSIMapEnumeratorNextNode(&enumerator);
+	}
+      GSIMapEndEnumerator(&enumerator);
+    }
+}
+
+- (NSUInteger) hash
+{
+  return map.nodeCount;
+}
+
+- (id) init
+{
+  return [self initWithObjects: 0 count: 0];
+}
+
+- (id) initWithCoder: (NSCoder*)aCoder
+{
+  if ([aCoder allowsKeyedCoding])
+    {
+      self = [super initWithCoder: aCoder];
+    }
+  else
+    {
+      unsigned	count;
+      id		value;
+      SEL		sel = @selector(decodeValueOfObjCType:at:);
+      IMP		imp = [aCoder methodForSelector: sel];
+      const char	*type = @encode(id);
+
+      (*imp)(aCoder, sel, @encode(unsigned), &count);
+
+      GSIMapInitWithZoneAndCapacity(&map, [self zone], count);
+      while (count-- > 0)
+        {
+	  (*imp)(aCoder, sel, type, &value);
+	  GSIMapAddKeyNoRetain(&map, (GSIMapKey)value);
+	}
+    }
+  return self;
+}
+
+/* Designated initialiser */
+- (id) initWithObjects: (const id*)objs count: (NSUInteger)c
+{
+  NSUInteger i;
+
+  GSIMapInitWithZoneAndCapacity(&map, [self zone], c);
+  for (i = 0; i < c; i++)
+    {
+      GSIMapNode     node;
+
+      if (objs[i] == nil)
+	{
+	  DESTROY(self);
+	  [NSException raise: NSInvalidArgumentException
+		      format: @"Tried to init set with nil value"];
+	}
+      node = GSIMapNodeForKey(&map, (GSIMapKey)objs[i]);
+      if (node == 0)
+	{
+	  GSIMapAddKey(&map, (GSIMapKey)objs[i]);
+        }
+    }
+  return self;
+}
+
+- (BOOL) intersectsSet: (NSSet*) otherSet
+{
+  Class	c;
+
+  /* If this set is empty, or the other is nil/empty,
+   * this method should return NO.
+   */
+  if (0 == map.nodeCount || nil == otherSet || [otherSet count] == 0)
+    {
+      return NO;
+    }
+
+  // Loop for all members in otherSet
+  c = object_getClass(otherSet);
+  if (c == setClass || c == mutableSetClass)
+    {
+      GSIMapTable		m = &((GSSet*)otherSet)->map;
+      GSIMapEnumerator_t	enumerator = GSIMapEnumeratorForMap(m);
+      GSIMapNode 		node = GSIMapEnumeratorNextNode(&enumerator);
+
+      while (node != 0)
+	{
+	  if (GSIMapNodeForKey(&map, node->key) != 0)
+	    {
+	      GSIMapEndEnumerator(&enumerator);
+	      return YES;
+	    }
+	  node = GSIMapEnumeratorNextNode(&enumerator);
+	}
+      GSIMapEndEnumerator(&enumerator);
+    }
+  else
+    {
+      NSEnumerator	*e;
+      id		o;
+
+      e = [otherSet objectEnumerator];
+      while ((o = [e nextObject])) // 1. pick a member from otherSet.
+	{
+	  if (GSIMapNodeForKey(&map, (GSIMapKey)o) != 0)
+	    {
+	      return YES;
+	    }
+	}
+    }
+  return NO;
+}
+
+- (BOOL) isSubsetOfSet: (NSSet*) otherSet
+{
+  GSIMapEnumerator_t	enumerator;
+  GSIMapNode 		node;
+  IMP			imp;
+
+  // -1. members of this set(self) <= that of otherSet
+  if (map.nodeCount > [otherSet count])
+    {
+      return NO;
+    }
+  if (map.nodeCount == 0)
+    {
+      return YES;
+    }
+
+  imp = [otherSet methodForSelector: memberSel];
+  enumerator = GSIMapEnumeratorForMap(&map);
+  node = GSIMapEnumeratorNextNode(&enumerator);
+
+  // 0. Loop for all members in this set(self).
+  while (node != 0)
+    {
+      // 1. check the member is in the otherSet.
+      if ((*imp)(otherSet, memberSel, node->key.obj) != nil)
+	{
+	  // 1.1 if true -> continue, try to check the next member.
+	  node = GSIMapEnumeratorNextNode(&enumerator);
+	}
+      else
+	{
+	  // 1.2 if false -> return NO;
+	  GSIMapEndEnumerator(&enumerator);
+	  return NO;
+	}
+    }
+  GSIMapEndEnumerator(&enumerator);
+  // 2. return YES; all members in this set are also in the otherSet.
+  return YES;
+}
+
+- (BOOL) isEqualToSet: (NSSet*)other
+{
+  if (other == nil)
+    {
+      return NO;
+    }
+  else if (other == self)
+    {
+      return YES;
+    }
+  else
+    {
+      Class	c = object_getClass(other);
+
+      if (c == setClass || c == mutableSetClass)
+	{
+	  if (map.nodeCount != ((GSSet*)other)->map.nodeCount)
+	    {
+	      return NO;
+	    }
+	  else if (map.nodeCount == 0)
+	    {
+	      return YES;
+	    }
+	  else
+	    {
+	      GSIMapEnumerator_t	enumerator;
+	      GSIMapNode 		node;
+
+	      enumerator = GSIMapEnumeratorForMap(&map);
+	      node = GSIMapEnumeratorNextNode(&enumerator);
+
+	      while (node != 0)
+		{
+		  if (GSIMapNodeForKey(&(((GSSet*)other)->map), node->key) == 0)
+		    {
+		      GSIMapEndEnumerator(&enumerator);
+		      return NO;
+		    }
+		  node = GSIMapEnumeratorNextNode(&enumerator);
+		}
+	      GSIMapEndEnumerator(&enumerator);
+	    }
+	}
+      else
+	{
+	  if (map.nodeCount != [other count])
+	    {
+	      return NO;
+	    }
+	  else if (map.nodeCount == 0)
+	    {
+	      return YES;
+	    }
+	  else
+	    {
+	      GSIMapEnumerator_t	enumerator;
+	      GSIMapNode 		node;
+	      IMP			imp;
+              IMP                       countImp;
+
+	      imp = [other methodForSelector: memberSel];
+              countImp = [other methodForSelector: privateCountOfSel];
+	      enumerator = GSIMapEnumeratorForMap(&map);
+	      node = GSIMapEnumeratorNextNode(&enumerator);
+
+	      while (node != 0)
+		{
+		  if ((*imp)(other, memberSel, node->key.obj) == nil)
+		    {
+		      GSIMapEndEnumerator(&enumerator);
+		      return NO;
+		    }
+                  else
+                    {
+                      NSUInteger c = (NSUInteger)
+                       countImp(other,privateCountOfSel,node->key.obj);
+                      // GSSet does not have duplicate entries
+                      if (c != 1)
+                        {
+                          return NO;
+                        }
+                    }
+		  node = GSIMapEnumeratorNextNode(&enumerator);
+		}
+	      GSIMapEndEnumerator(&enumerator);
+	    }
+	}
+      return YES;
+    }
+}
+
+- (BOOL) makeImmutable
+{
+  return YES;
+}
+
+- (void) makeObjectsPerform: (SEL)aSelector
+{
+  GSIMapEnumerator_t	enumerator = GSIMapEnumeratorForMap(&map);
+  GSIMapNode 		node = GSIMapEnumeratorNextNode(&enumerator);
+
+  while (node != 0)
+    {
+      [node->key.obj performSelector: aSelector];
+      node = GSIMapEnumeratorNextNode(&enumerator);
+    }
+  GSIMapEndEnumerator(&enumerator);
+}
+
+- (void) makeObjectsPerformSelector: (SEL)aSelector
+{
+  GSIMapEnumerator_t	enumerator = GSIMapEnumeratorForMap(&map);
+  GSIMapNode 		node = GSIMapEnumeratorNextNode(&enumerator);
+
+  while (node != 0)
+    {
+      [node->key.obj performSelector: aSelector];
+      node = GSIMapEnumeratorNextNode(&enumerator);
+    }
+  GSIMapEndEnumerator(&enumerator);
+}
+
+- (void) makeObjectsPerformSelector: (SEL)aSelector withObject: argument
+{
+  GSIMapEnumerator_t	enumerator = GSIMapEnumeratorForMap(&map);
+  GSIMapNode 		node = GSIMapEnumeratorNextNode(&enumerator);
+
+  while (node != 0)
+    {
+      [node->key.obj performSelector: aSelector withObject: argument];
+      node = GSIMapEnumeratorNextNode(&enumerator);
+    }
+  GSIMapEndEnumerator(&enumerator);
+}
+
+- (void) makeObjectsPerform: (SEL)aSelector withObject: argument
+{
+  GSIMapEnumerator_t	enumerator = GSIMapEnumeratorForMap(&map);
+  GSIMapNode 		node = GSIMapEnumeratorNextNode(&enumerator);
+
+  while (node != 0)
+    {
+      [node->key.obj performSelector: aSelector withObject: argument];
+      node = GSIMapEnumeratorNextNode(&enumerator);
+    }
+  GSIMapEndEnumerator(&enumerator);
+}
+
+- (id) member: (id)anObject
+{
+  if (anObject != nil)
+    {
+      GSIMapNode node = GSIMapNodeForKey(&map, (GSIMapKey)anObject);
+
+      if (node != 0)
+	{
+	  return node->key.obj;
+	}
+    }
+  return nil;
+}
+
+- (NSEnumerator*) objectEnumerator
+{
+  return AUTORELEASE([[GSSetEnumerator alloc] initWithSet: self]);
+}
+
+- (NSUInteger) countByEnumeratingWithState: (NSFastEnumerationState*)state
+                                   objects: (id*)stackbuf
+                                     count: (NSUInteger)len
+{
+  state->mutationsPtr = (unsigned long *)self;
+  return GSIMapCountByEnumeratingWithStateObjectsCount
+    (&map, state, stackbuf, len);
+}
+
+- (NSUInteger) sizeInBytesExcluding: (NSHashTable*)exclude
+{
+  NSUInteger	size = GSPrivateMemorySize(self, exclude);
+
+  if (size > 0)
+    {
+      GSIMapEnumerator_t	enumerator = GSIMapEnumeratorForMap(&map);
+      GSIMapNode 		node = GSIMapEnumeratorNextNode(&enumerator);
+
+      size += GSIMapSize(&map) - sizeof(map);
+      while (node != 0)
+        {
+          size += [node->key.obj sizeInBytesExcluding: exclude];
+          node = GSIMapEnumeratorNextNode(&enumerator);
+        }
+      GSIMapEndEnumerator(&enumerator);
+    }
+  return size;
+}
+
+@end
+
+@implementation GSMutableSet
+
++ (void) initialize
+{
+  if (self == [GSMutableSet class])
+    {
+      GSObjCAddClassBehavior(self, [GSSet class]);
+    }
+}
+
+- (void) addObject: (id)anObject
+{
+  GSIMapNode node;
+
+  if (anObject == nil)
+    {
+      [NSException raise: NSInvalidArgumentException
+		  format: @"Tried to add nil to set"];
+    }
+  node = GSIMapNodeForKey(&map, (GSIMapKey)anObject);
+  if (node == 0)
+    {
+      GSIMapAddKey(&map, (GSIMapKey)anObject);
+      _version++;
+    }
+}
+
+- (void) addObjectsFromArray: (NSArray*)array
+{
+  NSUInteger	count = [array count];
+
+  while (count-- > 0)
+    {
+      id	anObject = [array objectAtIndex: count];
+
+      if (anObject == nil)
+	{
+	  [NSException raise: NSInvalidArgumentException
+		      format: @"Tried to add nil to set"];
+	}
+      else
+	{
+	  GSIMapNode node;
+
+	  node = GSIMapNodeForKey(&map, (GSIMapKey)anObject);
+	  if (node == 0)
+	    {
+	      GSIMapAddKey(&map, (GSIMapKey)anObject);
+	      _version++;
+	    }
+	}
+    }
+}
+
+/* Override _version from GSSet */
+- (id) copyWithZone: (NSZone*)z
+{
+  NSSet	*copy = [setClass allocWithZone: z];
+
+  return [copy initWithSet: self copyItems: NO];
+}
+
+- (id) init
+{
+  return [self initWithCapacity: 0];
+}
+
+/* Designated initialiser */
+- (id) initWithCapacity: (NSUInteger)cap
+{
+  GSIMapInitWithZoneAndCapacity(&map, [self zone], cap);
+  return self;
+}
+
+- (id) initWithObjects: (const id*)objects
+		 count: (NSUInteger)count
+{
+  self = [self initWithCapacity: count];
+
+  while (count--)
+    {
+      id	anObject = objects[count];
+
+      if (anObject == nil)
+	{
+	  NSLog(@"Tried to init a set with a nil object");
+	  continue;
+	}
+      else
+	{
+	  GSIMapNode node;
+
+	  node = GSIMapNodeForKey(&map, (GSIMapKey)anObject);
+	  if (node == 0)
+	    {
+	      GSIMapAddKey(&map, (GSIMapKey)anObject);
+	    }
+	}
+    }
+  return self;
+}
+
+- (void) intersectSet: (NSSet*)other
+{
+  if (nil == other)
+    {
+      GSIMapCleanMap(&map);
+    }
+  else if (other != self && map.nodeCount > 0)
+    {
+      GSIMapEnumerator_t	enumerator;
+      GSIMapBucket		bucket;
+      GSIMapNode 		node;
+      Class                     c;
+
+      if (NO == [other isKindOfClass: [NSSet class]])
+        {
+	  [NSException raise: NSInvalidArgumentException
+		      format: @"-intersectSet: other object is not a set"];
+        }
+      if (0 == map.nodeCount)
+        {
+          return;                       // Already empty ... nothing to do
+        }
+      if (0 == [other count])
+        {
+          GSIMapCleanMap(&map);         // Other empty ... no intersection
+          return;
+        }
+
+      c = object_getClass(other);
+      if (c == setClass || c == mutableSetClass)
+        {
+          GSSet *o = (GSSet*)other;
+
+          enumerator = GSIMapEnumeratorForMap(&map);
+          bucket = GSIMapEnumeratorBucket(&enumerator);
+          node = GSIMapEnumeratorNextNode(&enumerator);
+
+          while (node != 0)
+            {
+              if (0 == GSIMapNodeForKey(&o->map, node->key))
+                {
+                  GSIMapRemoveNodeFromMap(&map, bucket, node);
+                  GSIMapFreeNode(&map, node);
+                }
+              bucket = GSIMapEnumeratorBucket(&enumerator);
+              node = GSIMapEnumeratorNextNode(&enumerator);
+            }
+          GSIMapEndEnumerator(&enumerator);
+        }
+      else
+        {
+	  SEL	sel = @selector(member:);
+	  IMP	imp = [other methodForSelector: sel];
+
+          enumerator = GSIMapEnumeratorForMap(&map);
+          bucket = GSIMapEnumeratorBucket(&enumerator);
+          node = GSIMapEnumeratorNextNode(&enumerator);
+
+          while (node != 0)
+            {
+              if (nil == (*imp)(other, sel, node->key.obj))
+                {
+                  GSIMapRemoveNodeFromMap(&map, bucket, node);
+                  GSIMapFreeNode(&map, node);
+                }
+              bucket = GSIMapEnumeratorBucket(&enumerator);
+              node = GSIMapEnumeratorNextNode(&enumerator);
+            }
+          GSIMapEndEnumerator(&enumerator);
+        }
+    }
+}
+
+- (BOOL) makeImmutable
+{
+  GSClassSwizzle(self, [GSSet class]);
+  return YES;
+}
+
+- (id) makeImmutableCopyOnFail: (BOOL)force
+{
+  GSClassSwizzle(self, [GSSet class]);
+  return self;
+}
+
+- (void) minusSet: (NSSet*) other
+{
+  if (other == self)
+    {
+      GSIMapCleanMap(&map);
+    }
+  else
+    {
+      NSEnumerator	*e = [other objectEnumerator];
+      id		anObject;
+
+      while ((anObject = [e nextObject]) != nil)
+	{
+	  GSIMapRemoveKey(&map, (GSIMapKey)anObject);
+	  _version++;
+	}
+    }
+}
+
+- (void) removeAllObjects
+{
+  GSIMapCleanMap(&map);
+}
+
+- (void) removeObject: (id)anObject
+{
+  if (anObject == nil)
+    {
+      NSWarnMLog(@"attempt to remove nil object");
+      return;
+    }
+  GSIMapRemoveKey(&map, (GSIMapKey)anObject);
+  _version++;
+}
+
+- (void) unionSet: (NSSet*) other
+{
+  if (other != self)
+    {
+      NSEnumerator	*e = [other objectEnumerator];
+
+      if (e != nil)
+	{
+	  id	anObject;
+	  SEL	sel = @selector(nextObject);
+	  IMP	imp = [e methodForSelector: sel];
+
+	  while ((anObject = (*imp)(e, sel)) != nil)
+	    {
+	      GSIMapNode node;
+
+	      node = GSIMapNodeForKey(&map, (GSIMapKey)anObject);
+	      if (node == 0)
+		{
+		  GSIMapAddKey(&map, (GSIMapKey)anObject);
+		  _version++;
+		}
+	    }
+	}
+    }
+}
+
+- (NSUInteger) countByEnumeratingWithState: (NSFastEnumerationState*)state
+                                   objects: (id*)stackbuf
+                                     count: (NSUInteger)len
+{
+  state->mutationsPtr = (unsigned long *)&_version;
+  return GSIMapCountByEnumeratingWithStateObjectsCount
+    (&map, state, stackbuf, len);
+}
+@end
+
+@interface	NSGSet : NSSet
+@end
+@implementation	NSGSet
+- (id) initWithCoder: (NSCoder*)aCoder
+{
+  NSLog(@"Warning - decoding archive containing obsolete %@ object - please delete/replace this archive", NSStringFromClass([self class]));
+  DESTROY(self);
+  self = (id)NSAllocateObject([GSSet class], 0, NSDefaultMallocZone());
+  self = [self initWithCoder: aCoder];
+  return self;
+}
+@end
+
+@interface	NSGMutableSet : NSMutableSet
+@end
+@implementation	NSGMutableSet
+- (id) initWithCoder: (NSCoder*)aCoder
+{
+  NSLog(@"Warning - decoding archive containing obsolete %@ object - please delete/replace this archive", NSStringFromClass([self class]));
+  DESTROY(self);
+  self = (id)NSAllocateObject([GSMutableSet class], 0, NSDefaultMallocZone());
+  self = [self initWithCoder: aCoder];
+  return self;
+}
+@end
+
diff --git a/Source/NSOrderedSet.m b/Source/NSOrderedSet.m
index 309fe0945..67c9255e7 100644
--- a/Source/NSOrderedSet.m
+++ b/Source/NSOrderedSet.m
@@ -39,16 +39,161 @@
 #import "GSFastEnumeration.h"
 #import "GSDispatch.h"
 
+@class	GSOrderedSet;
+@interface GSOrderedSet : NSObject	// Help the compiler
+@end
+@class	GSMutableOrderedSet;
+@interface GSMutableOrderedSet : NSObject	// Help the compiler
+@end
+
 @implementation NSOrderedSet
 
+static Class NSOrderedSet_abstract_class;
+static Class NSMutableOrderedSet_abstract_class;
+static Class NSOrderedSet_concrete_class;
+static Class NSMutableOrderedSet_concrete_class;
+
++ (id) allocWithZone: (NSZone*)z
+{
+  if (self == NSOrderedSet_abstract_class)
+    {
+      return NSAllocateObject(NSOrderedSet_concrete_class, 0, z);
+    }
+  else
+    {
+      return NSAllocateObject(self, 0, z);
+    }
+}
+
++ (void) initialize
+{
+  if (self == [NSOrderedSet class])
+    {
+      NSOrderedSet_abstract_class = self;
+      NSOrderedSet_concrete_class = [GSOrderedSet class];
+      [NSMutableSet class];
+    }
+}
+
 // NSCoding
 - (instancetype) initWithCoder: (NSCoder *)coder
 {
-  return nil;
+  Class		c;
+
+  c = object_getClass(self);
+  if (c == NSOrderedSet_abstract_class)
+    {
+      DESTROY(self);
+      self = [NSOrderedSet_concrete_class allocWithZone: NSDefaultMallocZone()];
+      return [self initWithCoder: coder];
+    }
+  else if (c == NSOrderedSet_abstract_class)
+    {
+      DESTROY(self);
+      self = [NSOrderedSet_concrete_class allocWithZone: NSDefaultMallocZone()];
+      return [self initWithCoder: coder];
+    }
+
+  if ([coder allowsKeyedCoding])
+    {
+      id	array;
+
+      array = [(NSKeyedUnarchiver*)coder _decodeArrayOfObjectsForKey:
+						@"NS.objects"];
+      if (array == nil)
+	{
+	  unsigned	i = 0;
+	  NSString	*key;
+	  id		val;
+
+	  array = [NSMutableArray arrayWithCapacity: 2];
+	  key = [NSString stringWithFormat: @"NS.object.%u", i];
+	  val = [(NSKeyedUnarchiver*)coder decodeObjectForKey: key];
+
+	  while (val != nil)
+	    {
+	      [array addObject: val];
+	      i++;
+	      key = [NSString stringWithFormat: @"NS.object.%u", i];
+	      val = [(NSKeyedUnarchiver*)coder decodeObjectForKey: key];
+	    }
+	}
+      self = [self initWithArray: array];
+    }
+  else
+    {
+      unsigned	count;
+
+      [coder decodeValueOfObjCType: @encode(unsigned) at: &count];
+      if (count > 0)
+        {
+	  unsigned	i;
+	  GS_BEGINIDBUF(objs, count);
+
+	  for (i = 0; i < count; i++)
+	    {
+	      [coder decodeValueOfObjCType: @encode(id) at: &objs[i]];
+	    }
+	  self = [self initWithObjects: objs count: count];
+	  while (count-- > 0)
+	    {
+	      [objs[count] release];
+	    }
+	  GS_ENDIDBUF();
+	}
+    }
+  return self;
 }
 
-- (void) encodeWithCoder: (NSCoder *)coder
+- (void) encodeWithCoder: (NSCoder *)aCoder
 {
+   if ([aCoder allowsKeyedCoding])
+    {
+      NSMutableArray *array = [NSMutableArray array];
+      NSEnumerator *en = [self objectEnumerator];
+      id obj = nil;
+      /* HACK ... MacOS-X seems to code differently if the coder is an
+       * actual instance of NSKeyedArchiver
+       */
+      
+      // Collect all objects...
+      while((obj = [en nextObject]) != nil)
+	{
+	  [array addObject: obj];
+	}
+      
+      if ([aCoder class] == [NSKeyedArchiver class])
+	{
+	  [(NSKeyedArchiver*)aCoder _encodeArrayOfObjects: array
+						   forKey: @"NS.objects"];
+	}
+      else
+	{
+	  unsigned	i = 0;
+	  NSEnumerator	*e = [self objectEnumerator];
+	  id		o;
+
+	  while ((o = [e nextObject]) != nil)
+	    {
+	      NSString	*key;
+
+	      key = [NSString stringWithFormat: @"NS.object.%u", i++];
+	      [(NSKeyedArchiver*)aCoder encodeObject: o forKey: key];
+	    }
+	}
+    }
+  else
+    {
+      unsigned		count = [self count];
+      NSEnumerator	*e = [self objectEnumerator];
+      id		o;
+
+      [aCoder encodeValueOfObjCType: @encode(unsigned) at: &count];
+      while ((o = [e nextObject]) != nil)
+	{
+	  [aCoder encodeValueOfObjCType: @encode(id) at: &o];
+	}
+    } 
 }
 
 - (id) copyWithZone: (NSZone*)zone
@@ -66,13 +211,14 @@
 				   objects: (__unsafe_unretained id[])stackbuf
 				     count: (NSUInteger)len
 {
+  [self subclassResponsibility: _cmd];
   return 0;
 }
 
 // class methods
 + (instancetype) orderedSet
 {
-  return nil;
+  return AUTORELEASE([[self allocWithZone: NSDefaultMallocZone()] init]);
 }
 
 + (instancetype) orderedSetWithArray:(NSArray *)objects