diff --git a/lib/setup.h b/lib/setup.h
index cd5f9d92ba37d06b908d3d86a5f68d45c0282714..a8b44134c2c2d63f74cbaf1bff24541c56b84269 100644
--- a/lib/setup.h
+++ b/lib/setup.h
@@ -112,10 +112,6 @@ typedef unsigned char bool;
 #include <floss.h>
 #endif
 
-#ifndef OS
-#error "There is no OS string defined!"
-#endif
-
 #if defined(HAVE_X509_H) && defined(HAVE_SSL_H) && defined(HAVE_RSA_H) && \
 defined(HAVE_PEM_H) && defined(HAVE_ERR_H) && defined(HAVE_CRYPTO_H) && \
 defined(HAVE_LIBSSL) && defined(HAVE_LIBCRYPTO)