diff --git a/src/include/lwip/opt.h b/src/include/lwip/opt.h
index f304e24c..2b5a765b 100644
--- a/src/include/lwip/opt.h
+++ b/src/include/lwip/opt.h
@@ -1086,7 +1086,7 @@
 #endif
 
 /** DNS maximum number of retries when asking for a name, before "timeout". */
-#ifndef DNS_MAX_RETRIES || defined __DOXYGEN__
+#if !defined DNS_MAX_RETRIES || defined __DOXYGEN__
 #define DNS_MAX_RETRIES           4
 #endif