--- a/apps/ocsp.c	2020-04-05 16:49:54.499380971 +0100
+++ b/apps/ocsp.c	2020-04-05 16:50:13.175380426 +0100
@@ -94,6 +94,10 @@
 #  endif
 # endif
 
+# if defined(OPENSSL_SYS_SERENITY)
+#  include <sys/select.h>
+# endif
+
 /* Maximum leeway in validity period: default 5 minutes */
 # define MAX_VALIDITY_PERIOD     (5 * 60)