diff --git a/include/libopencm3/usb/usbd.h b/include/libopencm3/usb/usbd.h
index fab63046..c73de072 100644
--- a/include/libopencm3/usb/usbd.h
+++ b/include/libopencm3/usb/usbd.h
@@ -65,6 +65,8 @@ extern u16 usbd_ep_read_packet(u8 addr, void *buf, u16 len);
 extern void usbd_ep_stall_set(u8 addr, u8 stall);
 extern u8 usbd_ep_stall_get(u8 addr);
 
+extern void usbd_ep_nak_set(u8 addr, u8 nak);
+
 /* Optional */
 extern void usbd_cable_connect(u8 on);
 
diff --git a/lib/usb/usb.c b/lib/usb/usb.c
index eb8e6d82..59c526dd 100644
--- a/lib/usb/usb.c
+++ b/lib/usb/usb.c
@@ -127,3 +127,9 @@ u8 usbd_ep_stall_get(u8 addr)
 {
 	return _usbd_device.driver->ep_stall_get(addr);
 }
+
+void usbd_ep_nak_set(u8 addr, u8 nak)
+{
+	_usbd_device.driver->ep_nak_set(addr, nak);
+}
+
diff --git a/lib/usb/usb_f103.c b/lib/usb/usb_f103.c
index ef97670f..19f645d1 100644
--- a/lib/usb/usb_f103.c
+++ b/lib/usb/usb_f103.c
@@ -30,10 +30,13 @@ static void stm32f103_ep_setup(u8 addr, u8 type, u16 max_size,
 static void stm32f103_endpoints_reset(void);
 static void stm32f103_ep_stall_set(u8 addr, u8 stall);
 static u8 stm32f103_ep_stall_get(u8 addr);
+static void stm32f103_ep_nak_set(u8 addr, u8 nak);
 static u16 stm32f103_ep_write_packet(u8 addr, const void *buf, u16 len);
 static u16 stm32f103_ep_read_packet(u8 addr, void *buf, u16 len);
 static void stm32f103_poll(void);
 
+static u8 force_nak[8];
+
 const struct _usbd_driver stm32f103_usb_driver = {
 	.init = stm32f103_usbd_init,
 	.set_address = stm32f103_set_address,
@@ -41,6 +44,7 @@ const struct _usbd_driver stm32f103_usb_driver = {
 	.ep_reset = stm32f103_endpoints_reset,
 	.ep_stall_set = stm32f103_ep_stall_set,
 	.ep_stall_get = stm32f103_ep_stall_get,
+	.ep_nak_set = stm32f103_ep_nak_set,
 	.ep_write_packet = stm32f103_ep_write_packet,
 	.ep_read_packet = stm32f103_ep_read_packet,
 	.poll = stm32f103_poll,
@@ -177,6 +181,20 @@ static u8 stm32f103_ep_stall_get(u8 addr)
 	return 0;
 }
 
+static void stm32f103_ep_nak_set(u8 addr, u8 nak)
+{
+	/* It does not make sence to force NAK on IN endpoints */
+	if(addr & 0x80)
+		return;
+
+	force_nak[addr] = nak;
+
+	if(nak)
+		USB_SET_EP_RX_STAT(addr, USB_EP_RX_STAT_NAK);
+	else
+		USB_SET_EP_RX_STAT(addr, USB_EP_RX_STAT_VALID);
+}
+
 /**
  * Copy a data buffer to packet memory.
  *
@@ -236,7 +254,8 @@ static u16 stm32f103_ep_read_packet(u8 addr, void *buf, u16 len)
 	usb_copy_from_pm(buf, USB_GET_EP_RX_BUFF(addr), len);
 	USB_CLR_EP_RX_CTR(addr);
 
-	USB_SET_EP_RX_STAT(addr, USB_EP_RX_STAT_VALID);
+	if(!force_nak[addr])
+		USB_SET_EP_RX_STAT(addr, USB_EP_RX_STAT_VALID);
 
 	return len;
 }
diff --git a/lib/usb/usb_f107.c b/lib/usb/usb_f107.c
index 9a20b0b3..f106a053 100644
--- a/lib/usb/usb_f107.c
+++ b/lib/usb/usb_f107.c
@@ -29,6 +29,8 @@
 #define RX_FIFO_SIZE	128
 static uint16_t fifo_mem_top;
 
+static u8 force_nak[4];
+
 static void stm32f107_usbd_init(void);
 static void stm32f107_set_address(u8 addr);
 static void stm32f107_ep_setup(u8 addr, u8 type, u16 max_size,
@@ -36,6 +38,7 @@ static void stm32f107_ep_setup(u8 addr, u8 type, u16 max_size,
 static void stm32f107_endpoints_reset(void);
 static void stm32f107_ep_stall_set(u8 addr, u8 stall);
 static u8 stm32f107_ep_stall_get(u8 addr);
+static void stm32f107_ep_nak_set(u8 addr, u8 nak);
 static u16 stm32f107_ep_write_packet(u8 addr, const void *buf, u16 len);
 static u16 stm32f107_ep_read_packet(u8 addr, void *buf, u16 len);
 static void stm32f107_poll(void);
@@ -51,6 +54,7 @@ const struct _usbd_driver stm32f107_usb_driver = {
 	.ep_reset = stm32f107_endpoints_reset,
 	.ep_stall_set = stm32f107_ep_stall_set,
 	.ep_stall_get = stm32f107_ep_stall_get,
+	.ep_nak_set = stm32f107_ep_nak_set,
 	.ep_write_packet = stm32f107_ep_write_packet,
 	.ep_read_packet = stm32f107_ep_read_packet,
 	.poll = stm32f107_poll,
@@ -210,6 +214,20 @@ static u8 stm32f107_ep_stall_get(u8 addr)
 		return (OTG_FS_DOEPCTL(addr) & OTG_FS_DOEPCTL0_STALL)?1:0;
 }
 
+static void stm32f107_ep_nak_set(u8 addr, u8 nak)
+{
+	/* It does not make sence to force NAK on IN endpoints */
+	if(addr & 0x80)
+		return;
+
+	force_nak[addr] = nak;
+
+	if(nak) 
+		OTG_FS_DOEPCTL(addr) |= OTG_FS_DOEPCTL0_SNAK;
+	else 
+		OTG_FS_DOEPCTL(addr) |= OTG_FS_DOEPCTL0_CNAK;
+}
+
 static u16 stm32f107_ep_write_packet(u8 addr, const void *buf, u16 len)
 {
 	const u32 *buf32 = buf;
@@ -256,7 +274,8 @@ static u16 stm32f107_ep_read_packet(u8 addr, void *buf, u16 len)
 	}
 
 	OTG_FS_DOEPTSIZ(addr) = doeptsiz[addr];
-	OTG_FS_DOEPCTL(addr) |= OTG_FS_DOEPCTL0_EPENA | OTG_FS_DOEPCTL0_CNAK;
+	OTG_FS_DOEPCTL(addr) |= OTG_FS_DOEPCTL0_EPENA | 
+		(force_nak[addr] ? OTG_FS_DOEPCTL0_SNAK : OTG_FS_DOEPCTL0_CNAK);
 
 	return len;
 }
diff --git a/lib/usb/usb_private.h b/lib/usb/usb_private.h
index 1bc6b3fc..40d59a11 100644
--- a/lib/usb/usb_private.h
+++ b/lib/usb/usb_private.h
@@ -78,6 +78,7 @@ struct _usbd_driver {
 	void (*ep_setup)(u8 addr, u8 type, u16 max_size, void (*cb)(u8 ep));
 	void (*ep_reset)(void);
 	void (*ep_stall_set)(u8 addr, u8 stall);
+	void (*ep_nak_set)(u8 addr, u8 nak);
 	u8 (*ep_stall_get)(u8 addr);
 	u16 (*ep_write_packet)(u8 addr, const void *buf, u16 len);
 	u16 (*ep_read_packet)(u8 addr, void *buf, u16 len);