diff --git a/_web_server/server/playground-server.scm b/_web_server/server/playground-server.scm
index 02ef2af..9c274f4 100755
--- a/_web_server/server/playground-server.scm
+++ b/_web_server/server/playground-server.scm
@@ -567,6 +567,7 @@
       (with-output-to-file command-file
         (lambda ()
           (println "+define+TESTBENCH")
+          (println "-CFLAGS -fcoroutines")
           (println "--timescale 1ps/1ps")
           (println "--top-module ~a" top)
           (println "--Mdir ~a" (path+ work-dir top))