diff --git a/lib/prism/polyfill/scan_byte.rb b/lib/prism/polyfill/scan_byte.rb
index 2def4572c4..9276e509fc 100644
--- a/lib/prism/polyfill/scan_byte.rb
+++ b/lib/prism/polyfill/scan_byte.rb
@@ -3,7 +3,7 @@
 require "strscan"
 
 # Polyfill for StringScanner#scan_byte, which didn't exist until Ruby 3.4.
-if !(StringScanner.instance_methods.include?(:scan_byte))
+if !(StringScanner.method_defined?(:scan_byte))
   StringScanner.include(
     Module.new {
       def scan_byte # :nodoc: