diff --git a/src/include/lwip/apps/mqtt_opts.h b/src/include/lwip/apps/mqtt_opts.h
index ffefacd2..4226d21e 100644
--- a/src/include/lwip/apps/mqtt_opts.h
+++ b/src/include/lwip/apps/mqtt_opts.h
@@ -39,7 +39,7 @@
 
 #include "lwip/opt.h"
 
-#ifdef	__cplusplus
+#ifdef __cplusplus
 extern "C" {
 #endif