diff --git a/common/rfb/CSecurityTLSBase.h b/common/rfb/CSecurityTLSBase.h
index 3839ebc..f7230b3 100644
--- a/common/rfb/CSecurityTLSBase.h
+++ b/common/rfb/CSecurityTLSBase.h
@@ -26,7 +26,9 @@
 #include <config.h>
 #endif
 
-#ifdef HAVE_GNUTLS
+#ifndef HAVE_GNUTLS
+#error "This header should not be compiled without HAVE_GNUTLS defined"
+#endif
 
 #include <rfb/CSecurity.h>
 #include <rfb/Security.h>
@@ -57,6 +59,4 @@
   };
 }
 
-#endif /* HAVE_GNUTLS */
-
 #endif