Index: generic/itclBase.c
==================================================================
--- generic/itclBase.c
+++ generic/itclBase.c
@@ -210,10 +210,11 @@
     ItclObjectInfo *infoPtr;
     const char * ret;
     char *res_option;
     int opt;
     int isNew;
+    Tcl_Class tclCls;
     Tcl_Object clazzObjectPtr, root;
     Tcl_Obj *objPtr, *resPtr;
 
     if (Tcl_InitStubs(interp, "8.6", 0) == NULL) {
         return TCL_ERROR;
@@ -340,14 +341,19 @@
 #ifdef NEW_PROTO_RESOLVER
     ItclVarsAndCommandResolveInit(interp);
 #endif
 
     objPtr = Tcl_NewStringObj("::oo::class", -1);
-    root = Tcl_NewObjectInstance(interp, Tcl_GetObjectAsClass(
-	    Tcl_GetObjectFromObj(interp, objPtr)), "::itcl::Root",
-	    NULL, 0, NULL, 0);
+    Tcl_IncrRefCount(objPtr);
+    clazzObjectPtr = Tcl_GetObjectFromObj(interp, objPtr);
+    if (!clazzObjectPtr || !(tclCls = Tcl_GetObjectAsClass(clazzObjectPtr))) {
+	Tcl_DecrRefCount(objPtr);
+        return TCL_ERROR;
+    }
     Tcl_DecrRefCount(objPtr);
+    root = Tcl_NewObjectInstance(interp, tclCls, "::itcl::Root",
+	    NULL, 0, NULL, 0);
 
     Tcl_NewMethod(interp, Tcl_GetObjectAsClass(root),
 	    Tcl_NewStringObj("unknown", -1), 0, &itclRootMethodType,
 	    ItclUnknownGuts);
     Tcl_NewMethod(interp, Tcl_GetObjectAsClass(root),
@@ -380,10 +386,11 @@
     /* work around for SF bug #254 needed because of problem in TclOO 1.0.2 !! */
     if (Tcl_PkgPresent(interp, "TclOO", "1.0.2", 1) != NULL) {
 	Itcl_IncrObjectRefCount(clazzObjectPtr);
     }
 
+    infoPtr->clazzObjectPtr = clazzObjectPtr;
     infoPtr->clazzClassPtr = Tcl_GetObjectAsClass(clazzObjectPtr);
 
     /*
      *  Initialize the ensemble package first, since we need this
      *  for other parts of [incr Tcl].
@@ -734,17 +741,27 @@
     }
     /* FIXME have to figure out why the refCount of
      * ::itcl::builtin::Info
      * and ::itcl::builtin::Info::vars and vars is 2 here !! */
     /* seems to be as the tclOO commands are not yet deleted ?? */
-    Tcl_DecrRefCount(infoPtr->infoVars3Ptr);
-    Tcl_DecrRefCount(infoPtr->infoVars4Ptr);
+    if (infoPtr->infoVars3Ptr) {
+	Tcl_DecrRefCount(infoPtr->infoVars3Ptr);
+    }
+    if (infoPtr->infoVars4Ptr) {
+	Tcl_DecrRefCount(infoPtr->infoVars4Ptr);
+    }
     if (checkMemoryLeaks) {
-        Tcl_DecrRefCount(infoPtr->infoVars3Ptr);
-        Tcl_DecrRefCount(infoPtr->infoVars4Ptr);
+        if (infoPtr->infoVars3Ptr) {
+	    Tcl_DecrRefCount(infoPtr->infoVars3Ptr);
+	}
+	if (infoPtr->infoVars4Ptr) {
+	    Tcl_DecrRefCount(infoPtr->infoVars4Ptr);
+	}
     /* see comment above */
     }
+    infoPtr->infoVars3Ptr = NULL;
+    infoPtr->infoVars4Ptr = NULL;
 
     Tcl_DecrRefCount(infoPtr->typeDestructorArgumentPtr);
 
     Tcl_EvalEx(infoPtr->interp,
             "::oo::define ::itcl::clazz deletemethod unknown", -1, 0);

Index: generic/itclClass.c
==================================================================
--- generic/itclClass.c
+++ generic/itclClass.c
@@ -245,10 +245,17 @@
     void *callbackPtr;
     int result;
     int newEntry;
     ItclResolveInfo *resolveInfoPtr;
     Tcl_Obj *cmdNamePtr;
+
+    if (!infoPtr->clazzClassPtr
+	|| Tcl_ObjectDeleted(infoPtr->clazzObjectPtr)
+    ) {
+	Tcl_AppendResult(interp, "oo-subsystem is deleted", NULL);
+	return TCL_ERROR;
+    }
 
     /*
      * check for an empty class name to avoid a crash
      */
     if (strlen(path) == 0) {

Index: generic/itclInt.h
==================================================================
--- generic/itclInt.h
+++ generic/itclInt.h
@@ -167,11 +167,11 @@
                                     /* type for getting the Itcl class info
                                      * from a TclOO Tcl_Object */
     const Tcl_ObjectMetadataType *object_meta_type;
                                     /* type for getting the Itcl object info
                                      * from a TclOO Tcl_Object */
-    Tcl_Object unused1;             /* the root object of Itcl */
+    Tcl_Object clazzObjectPtr;      /* the root object of Itcl */
     Tcl_Class clazzClassPtr;        /* the root class of Itcl */
     struct EnsembleInfo *ensembleInfo;
     struct ItclClass *currContextIclsPtr;
                                     /* context class for delegated option
                                      * handling */

Index: tests/sfbugs.test
==================================================================
--- tests/sfbugs.test
+++ tests/sfbugs.test
@@ -269,22 +269,81 @@
 
     [foo #auto] kerplunk hello world
 } -result {{foo0 kerplunk hello world} {foo0 kerplunk hello world} {foo0 kerplunk hello world}} \
   -cleanup {::itcl::delete class foo}
 
-test sfbug-254 { SF bug #254
+test sfbug-254.1 { SF bug #254 + bug [1dc2d851eb]
+} -body {
+    set interp [interp create]
+    set ::test_status ""
+    $interp eval {
+      oo::class destroy
+    }
+    lappend ::test_status "::oo::class destroy worked"
+    if {[catch {
+      $interp eval [::tcltest::loadScript]
+      $interp eval {
+        package require itcl
+      }
+    } msg]} {
+      lappend ::test_status $msg
+    }
+} -result {{::oo::class destroy worked} {::oo::class does not refer to an object}} \
+  -cleanup {interp delete $interp}
+
+test sfbug-254.2 { SF bug #254 + bug [1dc2d851eb]
+} -body {
+    set interp [interp create]
+    set ::test_status ""
+    $interp eval [::tcltest::loadScript]
+    $interp eval {
+      package require itcl
+
+      oo::class destroy
+    }
+    lappend ::test_status "::oo::class destroy worked"
+    if {[catch {
+      $interp eval {
+        ::itcl::class ::test {}
+      }
+    } msg]} {
+      lappend ::test_status $msg
+    }
+} -result {{::oo::class destroy worked} {oo-subsystem is deleted}} \
+  -cleanup {interp delete $interp}
+
+test sfbug-254.3 { delete oo-subsystem should remove all classes + summary of bug [1dc2d851eb]
 } -body {
     set interp [interp create]
+    set ::test_status ""
+    $interp eval [::tcltest::loadScript]
     $interp eval {
       package require itcl
 
-      set ::test_status ""
+      ::itcl::class ::test {}
+    }
+    lappend ::test_status "::test class created"
+    $interp eval {
       oo::class destroy
-      lappend ::test_status "::oo::class destroy worked"
+    }
+    lappend ::test_status "::oo::class destroy worked"
+    if {[catch {
+      $interp eval {
+        ::test x
+      }
+    } msg]} {
+      lappend ::test_status $msg
+    }
+    if {[catch {
+      $interp eval {
+        ::itcl::class ::test2 {inherit ::test}
+      }
+    } msg]} {
+      lappend ::test_status $msg
     }
-} -result {{::oo::class destroy worked}} \
-  -cleanup { }
+} -result {{::test class created} {::oo::class destroy worked} {invalid command name "::test"} {oo-subsystem is deleted}} \
+  -cleanup {interp delete $interp}
 
 test sfbug-255 { SF bug #255
 } -body {
     set ::test_status ""
 
@@ -365,10 +424,11 @@
   -cleanup {::itcl::delete class TestClass256}
 
 test sfbug-257 { SF bug #257
 } -body {
     set interp [interp create]
+    $interp eval [::tcltest::loadScript]
     $interp eval {
       package require itcl
       set ::test_status ""
       ::itcl::class ::cl1 {
         method m1 {} {