diff --git a/include/openssl/zuc_standard.h b/include/openssl/zuc_standard.h
index 9d75cd74..3bd74219 100644
--- a/include/openssl/zuc_standard.h
+++ b/include/openssl/zuc_standard.h
@@ -54,6 +54,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <openssl/e_os2.h>
 
 # ifdef  __cplusplus
 extern "C" {