diff --git a/firmware/libcommon/include/card_emu.h b/firmware/libcommon/include/card_emu.h
index c2d3b687..8edcecab 100644
--- a/firmware/libcommon/include/card_emu.h
+++ b/firmware/libcommon/include/card_emu.h
@@ -72,6 +72,7 @@ void card_emu_uart_wait_tx_idle(uint8_t uart_chan);
 void card_emu_uart_interrupt(uint8_t uart_chan);
 
 int card_emu_get_vcc(uint8_t uart_chan);
+bool card_ready(struct card_handle *ch);
 
 struct cardemu_usb_msg_config;
 int card_emu_set_config(struct card_handle *ch, const struct cardemu_usb_msg_config *scfg,
diff --git a/firmware/libcommon/source/card_emu.c b/firmware/libcommon/source/card_emu.c
index ab54fc5f..6b104130 100644
--- a/firmware/libcommon/source/card_emu.c
+++ b/firmware/libcommon/source/card_emu.c
@@ -215,6 +215,19 @@ struct card_handle {
 	} stats;
 };
 
+/* if the card should enque messages */
+bool card_ready(struct card_handle *ch)
+{
+	switch (ch->state) {
+	case ISO_S_IN_PTS:
+	case ISO_S_WAIT_TPDU:
+	case ISO_S_IN_TPDU:
+		return true;
+	default:
+		return false;
+	}
+}
+
 /* reset all the 'dynamic' state of the card handle to the initial/default values */
 static void card_handle_reset(struct card_handle *ch)
 {
diff --git a/firmware/libcommon/source/mode_cardemu.c b/firmware/libcommon/source/mode_cardemu.c
index a5485e4d..a0b4aa0f 100644
--- a/firmware/libcommon/source/mode_cardemu.c
+++ b/firmware/libcommon/source/mode_cardemu.c
@@ -736,6 +736,12 @@ static void dispatch_usb_command_cardem(struct msgb *msg, struct cardem_inst *ci
 	hdr = (struct simtrace_msg_hdr *) msg->l1h;
 	switch (hdr->msg_type) {
 	case SIMTRACE_MSGT_DT_CEMU_TX_DATA:
+		/* drop message when sim is in-active */
+		if (!card_ready(ci->ch)) {
+			/* FIXME: enqueue an error message for IN */
+			usb_buf_free(msg);
+			return;
+		}
 		queue = card_emu_get_uart_tx_queue(ci->ch);
 		llist_add_tail(&msg->list, queue);
 		card_emu_have_new_uart_tx(ci->ch);