diff --git a/Sources/OpenVPNAdapter/Libraries/Vendors/openvpn/client/ovpncli.hpp b/Sources/OpenVPNAdapter/Libraries/Vendors/openvpn/client/ovpncli.hpp
index 5aa12bf..06575a4 100644
--- a/Sources/OpenVPNAdapter/Libraries/Vendors/openvpn/client/ovpncli.hpp
+++ b/Sources/OpenVPNAdapter/Libraries/Vendors/openvpn/client/ovpncli.hpp
@@ -24,6 +24,9 @@
 // The crux of the API is defined in OpenVPNClient (below)
 // and TunBuilderBase.
 
+#ifndef OVPNCLI_HPP
+#define OVPNCLI_HPP
+
 #include <string>
 #include <vector>
 #include <utility>
@@ -605,3 +608,6 @@ namespace openvpn {
 
   }
 }
+
+#endif
+