diff --git a/lib/rb/benchmark/server.rb b/lib/rb/benchmark/server.rb
index e26e406..5162ac2 100644
--- a/lib/rb/benchmark/server.rb
+++ b/lib/rb/benchmark/server.rb
@@ -53,6 +53,7 @@
 # let our host know that the interpreter has started
 # ideally we'd wait until the server was serving, but we don't have a hook for that
 Marshal.dump(:started, STDOUT)
+STDOUT.flush
 
 host, port, serverklass = ARGV