diff --git a/lib/exec.c b/lib/exec.c
index 2a7ba93..39cdc14 100644
--- a/lib/exec.c
+++ b/lib/exec.c
@@ -3933,9 +3933,13 @@ static int execute (hcl_t* hcl)
 						/* 0(non-kernel object), 1(incomplete kernel object), 2(complete kernel object) */
 						if (HCL_OBJ_GET_FLAGS_KERNEL(class_obj) == 1)
 						{
-hcl_logbfmt (hcl, HCL_LOG_STDERR, ">>>%O c->sc=%O sc=%O b2=%d b3=%d nivars=%d ncvars=%d<<<\n", class_obj, class_obj->superclass, superclass, b2, b3, (int)HCL_OOP_TO_SMOOI(class_obj->nivars), (int)HCL_OOP_TO_SMOOI(class_obj->ncvars));
 							/* check if the new definition is compatible with kernel definition */
-							if (class_obj->superclass != superclass || HCL_OOP_TO_SMOOI(class_obj->nivars) != b2 || HCL_OOP_TO_SMOOI(class_obj->ncvars) != b3)
+							hcl_ooi_t spec, selfspec;
+
+							spec = HCL_OOP_TO_SMOOI(class_obj->spec);
+							selfspec = HCL_OOP_TO_SMOOI(class_obj->selfspec);
+hcl_logbfmt (hcl, HCL_LOG_STDERR, ">>>%O c->sc=%O sc=%O b2=%d b3=%d nivars=%d ncvars=%d<<<\n", class_obj, class_obj->superclass, superclass, b2, b3, (int)HCL_CLASS_SPEC_NAMED_INSTVARS(spec), (int)HCL_CLASS_SELFSPEC_CLASSVARS(spec));
+							if (class_obj->superclass != superclass || HCL_CLASS_SPEC_NAMED_INSTVARS(spec) != b2 || HCL_CLASS_SELFSPEC_CLASSVARS(selfspec) != b3)
 							{
 								hcl_seterrbfmt (hcl, HCL_EPERM, "incompatible redefintion of %.*js", HCL_OBJ_GET_SIZE(class_name), HCL_OBJ_GET_CHAR_SLOT(class_name));
 								if (do_throw_with_internal_errmsg(hcl, fetched_instruction_pointer) >= 0) break;
diff --git a/lib/gc.c b/lib/gc.c
index 01e4abb..34922af 100644
--- a/lib/gc.c
+++ b/lib/gc.c
@@ -1185,9 +1185,8 @@ static hcl_oop_class_t alloc_kernel_class (hcl_t* hcl, int class_flags, hcl_oow_
 	c->selfspec = HCL_SMOOI_TO_OOP(HCL_CLASS_SELFSPEC_MAKE(num_classvars, 0, class_flags));
 
 /* TODO: remove the following two duplicate fields with the spec fields */
-	c->nivars = HCL_SMOOI_TO_OOP(HCL_CLASS_SPEC_NAMED_INSTVARS(spec));
-	//c->nivars = HCL_SMOOI_TO_OOP(0);
-	c->ncvars = HCL_SMOOI_TO_OOP(num_classvars);
+	//c->nivars = HCL_SMOOI_TO_OOP(HCL_CLASS_SPEC_NAMED_INSTVARS(spec));
+	//c->ncvars = HCL_SMOOI_TO_OOP(num_classvars);
 	c->nivars_super = HCL_SMOOI_TO_OOP(0); /* TODO: encode it into spec? */
 	c->ibrand = HCL_SMOOI_TO_OOP(ibrand);
 
diff --git a/lib/hcl.h b/lib/hcl.h
index 2523279..f10ef32 100644
--- a/lib/hcl.h
+++ b/lib/hcl.h
@@ -858,7 +858,7 @@ struct hcl_process_scheduler_t
 };
 
 
-#define HCL_CLASS_NAMED_INSTVARS 11
+#define HCL_CLASS_NAMED_INSTVARS 9
 typedef struct hcl_class_t hcl_class_t;
 typedef struct hcl_class_t* hcl_oop_class_t;
 struct hcl_class_t
@@ -872,8 +872,6 @@ struct hcl_class_t
 	hcl_oop_t selfspec; /* SmallInteger. specification of the class object itself */
 
 	hcl_oop_t superclass;
-	hcl_oop_t nivars; /* SmallInteger. */
-	hcl_oop_t ncvars; /* SmallInteger. */
 	hcl_oop_t nivars_super; /* SmallInteger */
 	hcl_oop_t ibrand; /* SmallInteger */
 
diff --git a/lib/obj.c b/lib/obj.c
index 9901b81..1f0f6e1 100644
--- a/lib/obj.c
+++ b/lib/obj.c
@@ -488,14 +488,22 @@ hcl_oop_t hcl_makeclass (hcl_t* hcl, hcl_oop_t class_name, hcl_oop_t superclass,
 	/* TODO: other flags... indexable? byte? word?*/
 	spec = HCL_CLASS_SPEC_MAKE(nivars, 0, 0); /* TODO: how to include nivars_super ? */
 	selfspec = HCL_CLASS_SELFSPEC_MAKE(ncvars, 0, 0);
-	nivars_super = HCL_IS_NIL(hcl, superclass)? 0: HCL_OOP_TO_SMOOI(((hcl_oop_class_t)superclass)->nivars_super) + HCL_OOP_TO_SMOOI(((hcl_oop_class_t)superclass)->nivars);
+
+	if (!HCL_IS_NIL(hcl, superclass))
+	{
+		hcl_ooi_t superspec;
+		superspec = HCL_OOP_TO_SMOOI(((hcl_oop_class_t)superclass)->spec);
+		nivars_super = HCL_OOP_TO_SMOOI(((hcl_oop_class_t)superclass)->nivars_super) + HCL_CLASS_SPEC_NAMED_INSTVARS(superspec);
+	}
+	else
+	{
+		nivars_super = 0;
+	}
 
 	c->spec = HCL_SMOOI_TO_OOP(spec);
 	c->selfspec = HCL_SMOOI_TO_OOP(selfspec);
 	c->name = class_name;
 	c->superclass = superclass;
-	c->nivars = HCL_SMOOI_TO_OOP(nivars);
-	c->ncvars = HCL_SMOOI_TO_OOP(ncvars);
 	c->nivars_super = HCL_SMOOI_TO_OOP(nivars_super);
 	c->ibrand = HCL_SMOOI_TO_OOP(HCL_BRAND_INSTANCE); /* TODO: really need ibrand??? */