diff --git a/spec/ruby/optional/capi/ext/io_spec.c b/spec/ruby/optional/capi/ext/io_spec.c
index c60cd6e222..1c554a1a31 100644
--- a/spec/ruby/optional/capi/ext/io_spec.c
+++ b/spec/ruby/optional/capi/ext/io_spec.c
@@ -28,7 +28,7 @@ static int set_non_blocking(int fd) {
 }
 
 static int io_spec_get_fd(VALUE io) {
-#ifdef RUBY_VERSION_IS_3_3
+#ifdef RUBY_VERSION_IS_3_1
   return rb_io_descriptor(io);
 #else
   rb_io_t* fp;