diff --git a/src/openssl.hxx b/src/openssl.hxx
index 2d8772a..39e4326 100644
--- a/src/openssl.hxx
+++ b/src/openssl.hxx
@@ -24,17 +24,20 @@
 #ifndef OPENSSL_VERSION_NUMBER
 #  error OpenSSL Version Number not Found
 #elif OPENSSL_VERSION_NUMBER < 0x00908000L
-#  define OPENSSL_0
+#  warning OpenSSL older than 0.8 detected
+#  define OPENSSL_0_7
 #  define V0_CONST
 #  define CV_STACK
 #  define CV_X509
 #elif OPENSSL_VERSION_NUMBER < 0x10000000L
-#  define OPENSSL_0
+#  warning OpenSSL 0.8 detected
+#  define OPENSSL_0_8
 #  define V0_CONST const
 #  define CV_STACK
 #  define CV_X509
 #else
-#  define OPENSSL_1
+#  warning current OpenSSL 1.0 detected
+#  define OPENSSL_1_0
 #  define V0_CONST const
 #  define CV_STACK (_STACK*)
 #  define CV_X509 (STACK_OF(X509)*)