Index: generic/xotcl.c
===================================================================
diff -u -rbffe84bd5dccc0ed0d466bbf2d93bac783d49796 -r7c7a27874dbe5bb88a4261eef778b7fd29979761
--- generic/xotcl.c	(.../xotcl.c)	(revision bffe84bd5dccc0ed0d466bbf2d93bac783d49796)
+++ generic/xotcl.c	(.../xotcl.c)	(revision 7c7a27874dbe5bb88a4261eef778b7fd29979761)
@@ -7810,22 +7810,50 @@
 
 XOTCLINLINE static int
 changeClass(Tcl_Interp *interp, XOTclObject *obj, XOTclClass *cl) {
-  assert(obj);
+    assert(obj);
+    
+    if (cl != obj->cl) {
+        if (IsMetaClass(interp, cl)) {
+            /* Do not allow upgrading from a class to a meta-class (in
+               other words, don't make an object to a class). To allow
+               this, it would be necessary to reallocate the base
+               structures.
+            */
+            if (!IsMetaClass(interp, obj->cl)) {
+                return XOTclVarErrMsg(interp, "cannot change class of object ",
+                                      ObjStr(obj->cmdName),
+                                      " to metaclass ",
+                                      ObjStr(cl->object.cmdName),(char *) NULL);
+            }
+        } else {
+            /* The target class is not a meta class. Changing meta-class to 
+               meta-class, or class to class is fine, but downgrading requires
+               more work */
 
-  if (cl != obj->cl) {
-    if (IsMetaClass(interp, cl) && !IsMetaClass(interp, obj->cl)) {
-      return XOTclVarErrMsg(interp, "cannot change class of object ",
-                            ObjStr(obj->cmdName),
-                            " to metaclass ",
-                            ObjStr(cl->object.cmdName),(char *) NULL);
-    }
-    (void)RemoveInstance(obj, obj->cl);
-    AddInstance(obj, cl);
+            /*fprintf(stderr,"target class %s not a meta class, am i a class %d\n", 
+                    ObjStr(cl->object.cmdName),
+                    XOTclObjectIsClass(obj) );*/
 
-    MixinComputeDefined(interp, obj);
-    FilterComputeDefined(interp, obj);
-  }
-  return TCL_OK;
+            if (XOTclObjectIsClass(obj)) {
+                XOTclObjectClearClass(obj);
+                /* We are not done here yet.  We have to clear the
+                   class from class hierarchies etc., where an object
+                   is not allowed (e.g class hierarchies, mixin lists, etc.)
+                   
+                   We have to prohibit "Class class Object"
+                */
+
+                /*XXX*/                   
+
+            }
+        }
+        (void)RemoveInstance(obj, obj->cl);
+        AddInstance(obj, cl);
+        
+        MixinComputeDefined(interp, obj);
+        FilterComputeDefined(interp, obj);
+    }
+    return TCL_OK;
 }
 
 
Index: generic/xotclInt.h
===================================================================
diff -u -rbfeda566de60595825c75d78632d42458bb6cb05 -r7c7a27874dbe5bb88a4261eef778b7fd29979761
--- generic/xotclInt.h	(.../xotclInt.h)	(revision bfeda566de60595825c75d78632d42458bb6cb05)
+++ generic/xotclInt.h	(.../xotclInt.h)	(revision 7c7a27874dbe5bb88a4261eef778b7fd29979761)
@@ -447,6 +447,8 @@
 
 #define XOTclObjectSetClass(obj) \
 	(obj)->flags |= XOTCL_IS_CLASS
+#define XOTclObjectClearClass(obj) \
+	(obj)->flags &= ~XOTCL_IS_CLASS
 #define XOTclObjectIsClass(obj) \
 	((obj)->flags & XOTCL_IS_CLASS)
 #define XOTclObjectToClass(obj) \
Index: tests/testx.xotcl
===================================================================
diff -u -r34f178fae21c3cf3a2410c7b1986d3e6b84dcf42 -r7c7a27874dbe5bb88a4261eef778b7fd29979761
--- tests/testx.xotcl	(.../testx.xotcl)	(revision 34f178fae21c3cf3a2410c7b1986d3e6b84dcf42)
+++ tests/testx.xotcl	(.../testx.xotcl)	(revision 7c7a27874dbe5bb88a4261eef778b7fd29979761)
@@ -3185,6 +3185,31 @@
   ::errorCheck [Object ismetaclass M] 1 "is metaclass 1"
   ::errorCheck [Object ismetaclass C] 0 "is metaclass 0"
 
+  Class X
+  ::errorCheck [Object ismetaclass X] 0 "is metaclass 0"
+  ::errorCheck [X isclass] 1 "is isclass 1"
+  ::errorCheck [Class info instances X] ::X "is an instance of Class"
+  X class Object
+  ::errorCheck [X isclass] 0 "is isclass 0"
+  ::errorCheck [Class info instances X] "" "is not an instance of Class"
+  X destroy
+
+  Class M -superclass Class
+  M create m1
+  ::errorCheck [Object ismetaclass M] 1 "is metaclass 1"
+  ::errorCheck [M isclass] 1 "is isclass 1"
+  ::errorCheck [Class info instances M] ::M "is an instance of Class"
+  ::errorCheck [m1 info class] ::M "m1 is an instance of the meta-class"
+  ::errorCheck [m1 isclass] 1 "m1 is isclass 1"
+  M class Object
+  ::errorCheck [Object ismetaclass M] 0 "is metaclass 1"
+  ::errorCheck [M isclass] 0 "is isclass 0"
+  ::errorCheck [Class info instances M] "" "is not an instance of Class"
+  ::errorCheck [m1 info class] ::M "m1 is an instance of the meta-class"
+  ::errorCheck [m1 isclass] 1 "m1 is isclass 1"
+  
+  # to be completed XXX
+
   Class C -parameter {number name}
   C instproc test {} {
     my instvar {number x} name