diff --git a/internal/engine.cm b/internal/engine.cm
index 4d4fec46..efb901f2 100644
--- a/internal/engine.cm
+++ b/internal/engine.cm
@@ -312,9 +312,6 @@ var actor_mod = use_core('actor')
 var wota = use_core('wota')
 var nota = use_core('nota')
 
-function is_actor(value) {
-  return is_object(value) && value[ACTORDATA]
-}
 
 var ENETSERVICE = 0.1
 var REPLYTIMEOUT = 60 // seconds before replies are ignored
@@ -439,7 +436,6 @@ var race = pronto.race
 var sequence = pronto.sequence
 
 runtime_env.actor = actor
-runtime_env.is_actor = is_actor
 runtime_env.log = log
 runtime_env.send = send
 runtime_env.fallback = fallback
diff --git a/source/cell.c b/source/cell.c
index ad91899a..a0145e34 100644
--- a/source/cell.c
+++ b/source/cell.c
@@ -345,7 +345,8 @@ void script_startup(cell_rt *prt)
   tmp = js_core_json_use(js);
   JS_SetPropertyStr(js, env_ref.val, "json", tmp);
 
-  crt->actor_sym_ref.val = JS_NewString(js, "__ACTOR__");
+  crt->actor_sym_ref.val = JS_NewObject(js);
+  JS_CellStone(js, crt->actor_sym_ref.val);
   JS_SetActorSym(js, JS_DupValue(js, crt->actor_sym_ref.val));
   JS_SetPropertyStr(js, env_ref.val, "actorsym", JS_DupValue(js, crt->actor_sym_ref.val));
 
@@ -565,7 +566,8 @@ int cell_init(int argc, char **argv)
   cli_rt->on_exception_ref.val = JS_NULL;
   cli_rt->message_handle_ref.val = JS_NULL;
   cli_rt->unneeded_ref.val = JS_NULL;
-  cli_rt->actor_sym_ref.val = JS_NewString(ctx, "__ACTOR__");
+  cli_rt->actor_sym_ref.val = JS_NewObject(ctx);
+  JS_CellStone(ctx, cli_rt->actor_sym_ref.val);
   JS_SetActorSym(ctx, JS_DupValue(ctx, cli_rt->actor_sym_ref.val));
 
   root_cell = cli_rt;
diff --git a/source/runtime.c b/source/runtime.c
index e5a67b75..824b3489 100644
--- a/source/runtime.c
+++ b/source/runtime.c
@@ -11159,6 +11159,16 @@ static JSValue js_cell_is_object (JSContext *ctx, JSValue this_val, int argc, JS
   return JS_NewBool (ctx, mist_is_record (argv[0]));
 }
 
+/* is_actor(val) - true for actor objects (have actor_sym property) */
+static JSValue js_cell_is_actor (JSContext *ctx, JSValue this_val, int argc, JSValue *argv) {
+  if (argc < 1) return JS_FALSE;
+  JSValue val = argv[0];
+  if (!mist_is_record (val)) return JS_FALSE;
+  if (JS_IsNull (ctx->actor_sym)) return JS_FALSE;
+  int has = JS_HasPropertyKey (ctx, val, ctx->actor_sym);
+  return JS_NewBool (ctx, has > 0);
+}
+
 /* is_stone(val) - check if value is immutable */
 static JSValue js_cell_is_stone (JSContext *ctx, JSValue this_val, int argc, JSValue *argv) {
   (void)this_val;
@@ -11344,6 +11354,7 @@ static void JS_AddIntrinsicBaseObjects (JSContext *ctx) {
     js_set_global_cfunc(ctx, "is_null", js_cell_is_null, 1);
     js_set_global_cfunc(ctx, "is_number", js_cell_is_number, 1);
     js_set_global_cfunc(ctx, "is_object", js_cell_is_object, 1);
+    js_set_global_cfunc(ctx, "is_actor", js_cell_is_actor, 1);
     js_set_global_cfunc(ctx, "is_stone", js_cell_is_stone, 1);
     js_set_global_cfunc(ctx, "is_text", js_cell_is_text, 1);
     js_set_global_cfunc(ctx, "is_proto", js_cell_is_proto, 2);