diff --git a/src/openssl.hxx b/src/openssl.hxx
index 93bea71..d432299 100644
--- a/src/openssl.hxx
+++ b/src/openssl.hxx
@@ -13,6 +13,9 @@
 #include <openssl/x509.h>
 #include "openssl/bio.h"
 #include "openssl/des.h"
+#ifdef DATADIR // DATADIR is defined in autoconf/automake
+#undef DATADIR // but DATADIR is also a variablename in ssl.h
+#endif
 #include "openssl/ssl.h"
 #include <openssl/err.h>
 #include <vector>