diff --git a/lang/object.c b/lang/object.c
index 9a721b7..948903a 100644
--- a/lang/object.c
+++ b/lang/object.c
@@ -99,11 +99,17 @@
 }
 
 void object_list_set(VmState state, ObjectList list, int index, Object obj) {
+	vm_abort_if(state, index < 0, "object_list_get: index too small");
+	vm_abort_if(state, index >= list->length,
+		"object_list_get: index too large");
 	object_drop(state, &(list->elems[index]));
 	list->elems[index] = obj;
 }
 
 Object object_list_get(VmState state, ObjectList list, int index) {
+	vm_abort_if(state, index < 0, "object_list_get: index too small");
+	vm_abort_if(state, index >= list->length,
+		"object_list_get: index too large");
 	Object obj = list->elems[index];
 	object_hold(state, obj);
 	return obj;