diff --git a/yjit.rb b/yjit.rb
index cd3ad4d652..6f7fdb41b3 100644
--- a/yjit.rb
+++ b/yjit.rb
@@ -6,7 +6,7 @@ module YJIT
       blocks = YJIT.blocks_for(iseq)
       return if blocks.empty?
 
-      str = ""
+      str = String.new
       str << iseq.disasm
       str << "\n"