diff --git a/devices/air724/air724.c b/devices/air724/air724.c
index 1bb575de..5f334dfa 100644
--- a/devices/air724/air724.c
+++ b/devices/air724/air724.c
@@ -386,7 +386,7 @@ static int air724_recv(int id, void *buf, size_t len)
 int air724_send(int id, const void *buf, size_t len)
 {
     at_echo_t echo;
-    char expect_str[10];
+    char expect_str[30];
 
     if (tos_at_global_lock_pend() != 0) {
         return -1;