diff --git a/build.rb b/build.rb
index 4c6a674..a2883e3 100644
--- a/build.rb
+++ b/build.rb
@@ -72,7 +72,7 @@ def fetch(url, name = nil)
 end
 
 # https://bugs.ruby-lang.org/issues/18658
-if stack == "heroku-22" && version.starts_with?("3.0")
+if stack == "heroku-22" && version.start_with?("3.0")
   raise "Cannot build Ruby 3.0 on heroku-22"
 end