diff --git a/firmware/libcommon/source/card_emu.c b/firmware/libcommon/source/card_emu.c
index 5298ffcf..497b963e 100644
--- a/firmware/libcommon/source/card_emu.c
+++ b/firmware/libcommon/source/card_emu.c
@@ -254,12 +254,35 @@ void usb_buf_upd_len_and_submit(struct msgb *msg)
 /* Allocate USB buffer and push + initialize simtrace_msg_hdr */
 struct msgb *usb_buf_alloc_st(uint8_t ep, uint8_t msg_class, uint8_t msg_type)
 {
-	struct msgb *msg;
+	struct msgb *msg = NULL;
 	struct simtrace_msg_hdr *sh;
 
-	msg = usb_buf_alloc(ep);
-	if (!msg)
-		return NULL;
+	while (!msg) {
+		msg = usb_buf_alloc(ep); // try to allocate some memory
+		if (!msg) { // allocation failed, we might be out of memory
+			struct llist_head *queue = usb_get_queue(ep);
+			if (!queue) {
+				TRACE_ERROR("ep %u: %s queue does not exist\n\r",
+				            ep, __func__);
+				return NULL;
+			}
+			if (llist_empty(queue)) {
+				TRACE_ERROR("ep %u: %s EOMEM (queue already empty)\n\r",
+				            ep, __func__);
+				return NULL;
+			}
+			msg = msgb_dequeue(queue);
+			if (!msg) {
+				TRACE_ERROR("ep %u: %s no msg in non-empty queue\n\r",
+				            ep, __func__);
+				return NULL;
+			}
+			usb_buf_free(msg);
+			msg = NULL;
+			TRACE_DEBUG("ep %u: %s queue msg dropped\n\r",
+			            ep, __func__);
+		}
+	}
 
 	msg->l1h = msgb_put(msg, sizeof(*sh));
 	sh = (struct simtrace_msg_hdr *) msg->l1h;