diff --git a/ethermess-backend.c b/ethermess-backend.c
index 31ce771..2ec6d27 100644
--- a/ethermess-backend.c
+++ b/ethermess-backend.c
@@ -441,6 +441,10 @@ void read_status(void) {
 }
 
 void read_message(void) {
+	if (own_message_send_state != IDLE) {
+		errx(1, "Frontend sent a new message while we are still processing the old one");
+	}
+
 	unsigned char mac[6];
 	readallx(0, mac, sizeof(mac));