diff --git a/common/rfb/SSecurityTLSBase.h b/common/rfb/SSecurityTLSBase.h
index 4daad21..b1f2d44 100644
--- a/common/rfb/SSecurityTLSBase.h
+++ b/common/rfb/SSecurityTLSBase.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/SSecurity.h>
 #include <rdr/InStream.h>
@@ -57,6 +59,4 @@
 
 }
 
-#endif /* HAVE_GNUTLS */
-
 #endif