diff --git a/gtk2_ardour/system_exec.cc b/gtk2_ardour/system_exec.cc
index a01351c92e..889b1565ad 100644
--- a/gtk2_ardour/system_exec.cc
+++ b/gtk2_ardour/system_exec.cc
@@ -658,6 +658,7 @@ SystemExec::write_to_stdin(std::string d, size_t len)
 		}
 		c += r;
 	}
+	fsync(pin[1]);
 	::pthread_mutex_unlock(&write_lock);
 	return c;
 }