diff --git a/binding-mruby/binding-mruby.cpp b/binding-mruby/binding-mruby.cpp
index 9da48d7..47465af 100644
--- a/binding-mruby/binding-mruby.cpp
+++ b/binding-mruby/binding-mruby.cpp
@@ -118,7 +118,7 @@ static mrb_value
 mkxpTimeOp(mrb_state *mrb, mrb_value)
 {
 	mrb_int iterations = 1;
-	const char *opName = 0;
+	const char *opName = "";
 	mrb_value block;
 
 	mrb_get_args(mrb, "|iz&", &iterations, &opName, &block);