diff --git a/flight/pios/stm32f10x/pios_usb_cdc.c b/flight/pios/stm32f10x/pios_usb_cdc.c
index 1a04f00f5..c321afab5 100644
--- a/flight/pios/stm32f10x/pios_usb_cdc.c
+++ b/flight/pios/stm32f10x/pios_usb_cdc.c
@@ -69,7 +69,12 @@ struct pios_usb_cdc_dev {
 	uint32_t tx_out_context;
 
 	uint8_t rx_packet_buffer[PIOS_USB_BOARD_CDC_DATA_LENGTH];
-	uint8_t tx_packet_buffer[PIOS_USB_BOARD_CDC_DATA_LENGTH];
+	/*
+	 * NOTE: This is -1 as somewhat of a hack.  It ensures that we always send packets
+	 * that are strictly < maxPacketSize for this interface which means we never have
+	 * to bother with zero length packets (ZLP).
+	 */
+	uint8_t tx_packet_buffer[PIOS_USB_BOARD_CDC_DATA_LENGTH - 1];
 
 	uint32_t rx_dropped;
 	uint32_t rx_oversize;
diff --git a/flight/pios/stm32f4xx/pios_usb_cdc.c b/flight/pios/stm32f4xx/pios_usb_cdc.c
index 0b47c880b..cb0ce9bc7 100644
--- a/flight/pios/stm32f4xx/pios_usb_cdc.c
+++ b/flight/pios/stm32f4xx/pios_usb_cdc.c
@@ -73,7 +73,12 @@ struct pios_usb_cdc_dev {
 	uint8_t rx_packet_buffer[PIOS_USB_BOARD_CDC_DATA_LENGTH] __attribute__ ((aligned(4)));
 	volatile bool rx_active;
 
-	uint8_t tx_packet_buffer[PIOS_USB_BOARD_CDC_DATA_LENGTH] __attribute__ ((aligned(4)));
+	/*
+	 * NOTE: This is -1 as somewhat of a hack.  It ensures that we always send packets
+	 * that are strictly < maxPacketSize for this interface which means we never have
+	 * to bother with zero length packets (ZLP).
+	 */
+	uint8_t tx_packet_buffer[PIOS_USB_BOARD_CDC_DATA_LENGTH - 1] __attribute__ ((aligned(4)));
 	volatile bool tx_active;
 
 	uint8_t ctrl_tx_packet_buffer[PIOS_USB_BOARD_CDC_MGMT_LENGTH] __attribute__ ((aligned(4)));