diff --git a/src/openssl-engine.hxx b/src/openssl-engine.hxx
index e7b8e9b..adff922 100644
--- a/src/openssl-engine.hxx
+++ b/src/openssl-engine.hxx
@@ -18,6 +18,7 @@
 #  define OPENSSL_V0_CONST const
 #endif
 
+#undef DATADIR
 #include <openssl/engine.h>
 #include <map>
 #include <string>
diff --git a/src/pcsc.hxx b/src/pcsc.hxx
index 6fedac0..1c2c4ae 100644
--- a/src/pcsc.hxx
+++ b/src/pcsc.hxx
@@ -35,6 +35,7 @@
 
 #ifdef WIN32
   #undef UNICODE
+  #undef DATADIR
   #include <WinSCard.h>
   #undef ERROR
   #ifndef MAX_ATR_SIZE