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 */
diff --git a/common/rfb/CSecurityTLS.h b/common/rfb/CSecurityTLS.h
index a2bcc57..9e5ed72 100644
--- a/common/rfb/CSecurityTLS.h
+++ b/common/rfb/CSecurityTLS.h
@@ -26,7 +26,9 @@
 #include <config.h>
 #endif
 
-#ifdef HAVE_GNUTLS
+#ifndef HAVE_GNUTLS
+#error "This header should not be included without HAVE_GNUTLS defined"
+#endif
 
 #include <rfb/CSecurityTLSBase.h>
 #include <rfb/SSecurityVeNCrypt.h>
@@ -48,6 +50,4 @@
   };
 }
 
-#endif /* HAVE_GNUTLS */
-
 #endif /* __C_SECURITY_TLS_H__ */
diff --git a/common/rfb/CSecurityTLSBase.cxx b/common/rfb/CSecurityTLSBase.cxx
index 0755f36..289015a 100644
--- a/common/rfb/CSecurityTLSBase.cxx
+++ b/common/rfb/CSecurityTLSBase.cxx
@@ -23,7 +23,9 @@
 #include <config.h>
 #endif
 
-#ifdef HAVE_GNUTLS
+#ifndef HAVE_GNUTLS
+#error "This header should not be compiled without HAVE_GNUTLS defined"
+#endif
 
 #include <rfb/CSecurityTLSBase.h>
 #include <rfb/CConnection.h>
@@ -136,4 +138,3 @@
   return true;
 }
 
-#endif /* HAVE_GNUTLS */
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