diff --git a/common/rfb/CSecurityTLS.cxx b/common/rfb/CSecurityTLS.cxx
index 6bd2fa7..ae095fa 100644
--- a/common/rfb/CSecurityTLS.cxx
+++ b/common/rfb/CSecurityTLS.cxx
@@ -23,11 +23,12 @@
 #include <config.h>
 #endif
 
-#ifdef HAVE_GNUTLS
+#ifndef HAVE_GNUTLS
+#error "This source should not be compiled without HAVE_GNUTLS defined"
+#endif
 
 #include <rfb/CSecurityTLS.h>
 
-
 using namespace rfb;
 
 CSecurityTLS::CSecurityTLS() :  anon_cred(0)
@@ -63,4 +64,3 @@
 
 }
 
-#endif /* HAVE_GNUTLS */