diff --git a/crypto/bn/bn.h b/crypto/bn/bn.h
index 7129d3698..218907b8c 100644
--- a/crypto/bn/bn.h
+++ b/crypto/bn/bn.h
@@ -68,7 +68,7 @@
 extern "C" {
 #endif
 
-#ifdef VMS
+#ifdef OPENSSL_SYS_VMS
 #undef BN_LLONG /* experimental, so far... */
 #endif