diff --git a/nsock/src/nsock_log.h b/nsock/src/nsock_log.h
index ddc7239fe..589206846 100644
--- a/nsock/src/nsock_log.h
+++ b/nsock/src/nsock_log.h
@@ -95,7 +95,7 @@
 
 void __nsock_log_internal(nsock_pool nsp, nsock_loglevel_t loglevel,
                           const char *file, int line, const char *func,
-                          const char *format, ...);
+                          const char *format, ...) __attribute__((format (printf, 6, 7)));
 
 void nsock_stderr_logger(nsock_pool nsp, const struct nsock_log_rec *rec);