diff --git a/lynglib/src/commonMain/kotlin/net/sergeych/lyng/Scope.kt b/lynglib/src/commonMain/kotlin/net/sergeych/lyng/Scope.kt
index 828e32e..26933e2 100644
--- a/lynglib/src/commonMain/kotlin/net/sergeych/lyng/Scope.kt
+++ b/lynglib/src/commonMain/kotlin/net/sergeych/lyng/Scope.kt
@@ -898,4 +898,10 @@ open class Scope(
         fun new(): Scope =
             Script.defaultImportManager.copy().newModuleAt(Pos.builtIn)
     }
+
+    fun requireClass(name: String): net.sergeych.lyng.obj.ObjClass {
+        val rec = get(name) ?: raiseSymbolNotFound(name)
+        return rec.value as? net.sergeych.lyng.obj.ObjClass
+            ?: raiseClassCastError("Expected class $name, got ${rec.value.objClass.className}")
+    }
 }
diff --git a/lynglib/src/commonMain/kotlin/net/sergeych/lyng/Script.kt b/lynglib/src/commonMain/kotlin/net/sergeych/lyng/Script.kt
index 2d571e9..eab188c 100644
--- a/lynglib/src/commonMain/kotlin/net/sergeych/lyng/Script.kt
+++ b/lynglib/src/commonMain/kotlin/net/sergeych/lyng/Script.kt
@@ -563,9 +563,7 @@ class Script(
             ImportManager(rootScope, SecurityManager.allowAll).apply {
                 addPackage("lyng.stdlib") { module ->
                     module.eval(Source("lyng.stdlib", rootLyng))
-                    val cls = module["KotlinIterator"]?.value as? ObjClass
-                        ?: module.raiseSymbolNotFound("KotlinIterator")
-                    ObjKotlinIterator.bindTo(cls)
+                    ObjKotlinIterator.bindTo(module.requireClass("KotlinIterator"))
                 }
                 addPackage("lyng.buffer") {
                     it.addConstDoc(