diff --git a/src/openssl-compatibility.hxx b/src/openssl-compatibility.hxx
index 71c5bd8..b43c541 100644
--- a/src/openssl-compatibility.hxx
+++ b/src/openssl-compatibility.hxx
@@ -5,6 +5,7 @@
 //       1         2         3         4         5         6         7         8
 // 45678901234567890123456789012345678901234567890123456789012345678901234567890
 
+#undef DATADIR
 #include <openssl/opensslv.h>
 #ifndef OPENSSL_VERSION_NUMBER
 #  error OpenSSL Version Number not Found