diff --git a/apps/smtp/smtp.c b/apps/smtp/smtp.c
index 612785a..85481c1 100644
--- a/apps/smtp/smtp.c
+++ b/apps/smtp/smtp.c
@@ -199,7 +199,7 @@ enum smtp_session_state {
   SMTP_CLOSED
 };
 
-#if LWIP_DEBUG
+#ifdef LWIP_DEBUG
 /** State-to-string table for debugging */
 const char *smtp_state_str[] = {
   "SMTP_NULL",
@@ -299,7 +299,7 @@ static void   smtp_send_body(struct smtp_session *s, struct tcp_pcb *pcb);
 static void   smtp_process(void *arg, struct tcp_pcb *pcb, struct pbuf *p);
 
 
-#if LWIP_DEBUG
+#ifdef LWIP_DEBUG
 /** Convert an smtp result to a string */
 const char*
 smtp_result_str(u8_t smtp_result)
diff --git a/apps/smtp/smtp.h b/apps/smtp/smtp.h
index d6c2ced..4b9b9d9 100644
--- a/apps/smtp/smtp.h
+++ b/apps/smtp/smtp.h
@@ -60,7 +60,7 @@ err_t smtp_send_mail(const char *from, const char* to, const char* subject, cons
 err_t smtp_send_mail_static(const char *from, const char* to, const char* subject, const char* body,
                      smtp_result_fn callback_fn, void* callback_arg);
 void smtp_send_mail_int(void *arg);
-#if LWIP_DEBUG
+#ifdef LWIP_DEBUG
 const char* smtp_result_str(u8_t smtp_result);
 #endif