diff --git a/ethermess-backend.c b/ethermess-backend.c
index 708a103..b608f57 100644
--- a/ethermess-backend.c
+++ b/ethermess-backend.c
@@ -844,6 +844,10 @@ void handle_ack(const unsigned char source_mac[6], const unsigned char *data, si
 		err(1, "printf");
 	}
 
+	if (fflush(stdout) == EOF) {
+		err(1, "fflush");
+	}
+
 	if (own_message_send_state == WAITING_ACK && msgid == own_message_msgid) {
 		own_message_send_state = IDLE;
 	}