diff --git a/minproto.leg b/minproto.leg
index 8de41cd..a6e5432 100644
--- a/minproto.leg
+++ b/minproto.leg
@@ -1,6 +1,6 @@
 # minproto.leg -- minimal prototype langauge for semantic experiments
 #
-# last edited: 2024-05-09 11:30:35 by piumarta on zora-1034.local
+# last edited: 2024-05-09 13:59:36 by piumarta on zora-1034.local
 
 %{
 ;
@@ -160,6 +160,8 @@ union object _nil = { Undefined };
 
 #define nil (&_nil)
 
+#define UNDEFINED 0
+
 enum type getType(oop obj)
 {
 # if TAGS
@@ -393,7 +395,7 @@ oop newSymbol(char *name)
 {
     oop obj = make(Symbol);
     _set(obj, Symbol,name,  strdup(name));
-    _set(obj, Symbol,value, nil);
+    _set(obj, Symbol,value, UNDEFINED);
     return obj;
 }
 
@@ -566,7 +568,7 @@ oop Object_get(oop obj, oop key)
 	if (ind >= 0) return _get(o, Object,properties)[ind].val;
 	o = _getDelegate(o);
     }
-    fatal("%s.%s is undefined", storeString(obj, 0), storeString(key, 0));
+    fatal("undefined property: %s.%s", storeString(obj, 0), storeString(key, 0));
     return nil;
 }
 
@@ -577,7 +579,9 @@ oop getvar(oop obj, oop key)
 	if (ind >= 0) return _get(obj, Object,properties)[ind].val;
 	obj = _getDelegate(obj);
     }
-    return is(Symbol, key) ? _get(key, Symbol,value) : nil;
+    oop value = _get(key, Symbol,value); // asserts is(Symbol,key)
+    if (!value) fatal("undefined variable: %s", storeString(key, 0));
+    return value;
 }
 
 oop setvar(oop obj, oop key, oop val)
@@ -1250,8 +1254,7 @@ oop Invoke_eval(oop exp, oop env)
     oop self  = eval  (Object_get(exp, sym_self     ), env);
     oop meth  =        Object_get(exp, sym_method   )       ;
     oop iargs = evargs(Object_get(exp, sym_arguments), env);
-    oop ifunc = Object_get(self, meth);
-    if (nil == ifunc) fatal("%s.%s is undefined", storeString(self, 0), storeString(meth, 0));
+    oop ifunc = Object_get(self, meth); // fails if property not defined
     return apply(ifunc, self, iargs, env);
 }