diff --git a/src/njs_function.c b/src/njs_function.c
--- a/src/njs_function.c
+++ b/src/njs_function.c
@@ -1427,6 +1427,20 @@ njs_function_prototype_apply(njs_vm_t *vm, njs_value_t *args, njs_uint_t nargs,
 
     frame = (njs_frame_t *) vm->top_frame;
 
+    if (njs_slow_path(args == NULL && length != 0)) {
+        njs_stderror("APPLY-INVARIANT null argument vector for %d "
+                     "arguments\n", (int) length);
+        abort();
+    }
+
+    for (i = 0; i < length; i++) {
+        if (njs_slow_path(!njs_is_valid(&args[i]))) {
+            njs_stderror("APPLY-INVARIANT absent-element marker at "
+                         "argument %d\n", (int) i);
+            abort();
+        }
+    }
+
     ret = njs_function_frame(vm, func, this, args, length, 0);
     if (njs_slow_path(ret != NJS_OK)) {
         return ret;