diff --git a/OpenVPN Adapter/Vendors/openvpn/client/ovpncli.hpp b/OpenVPN Adapter/Vendors/openvpn/client/ovpncli.hpp
index 3059d09..5aa4bf1 100644
--- a/OpenVPN Adapter/Vendors/openvpn/client/ovpncli.hpp	
+++ b/OpenVPN Adapter/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>
@@ -600,3 +603,5 @@ namespace openvpn {
 
   }
 }
+
+#endif