diff --git a/os/hal/src/serial_usb.c b/os/hal/src/serial_usb.c
index 5fec52a68..52be6e975 100644
--- a/os/hal/src/serial_usb.c
+++ b/os/hal/src/serial_usb.c
@@ -288,8 +288,8 @@ void sduDataTransmitted(USBDriver *usbp, usbep_t ep) {
 
   (void)ep;
 
-  chnAddFlagsI(sdup, CHN_OUTPUT_EMPTY);
   chSysLockFromIsr();
+  chnAddFlagsI(sdup, CHN_OUTPUT_EMPTY);
 
   if ((n = chOQGetFullI(&sdup->oqueue)) > 0) {
     /* The endpoint cannot be busy, we are in the context of the callback,
@@ -321,8 +321,8 @@ void sduDataReceived(USBDriver *usbp, usbep_t ep) {
 
   (void)ep;
 
-  chnAddFlagsI(sdup, CHN_INPUT_AVAILABLE);
   chSysLockFromIsr();
+  chnAddFlagsI(sdup, CHN_INPUT_AVAILABLE);
 
   /* Writes to the input queue can only happen when there is enough space
      to hold at least one packet.*/
diff --git a/testhal/STM32F4xx/USB_CDC/main.c b/testhal/STM32F4xx/USB_CDC/main.c
index e36ce3dc9..0ae9c81e0 100644
--- a/testhal/STM32F4xx/USB_CDC/main.c
+++ b/testhal/STM32F4xx/USB_CDC/main.c
@@ -225,6 +225,11 @@ static const USBDescriptor *get_descriptor(USBDriver *usbp,
   return NULL;
 }
 
+/**
+ * @brief   IN EP1 state.
+ */
+static USBInEndpointState ep1instate;
+
 /**
  * @brief   EP1 initialization structure (IN only).
  */
@@ -235,11 +240,16 @@ static const USBEndpointConfig ep1config = {
   NULL,
   0x0040,
   0x0000,
-  NULL,
+  &ep1instate,
   NULL,
   NULL
 };
 
+/**
+ * @brief   OUT EP1 state.
+ */
+USBOutEndpointState ep1outstate;
+
 /**
  * @brief   EP2 initialization structure (IN only).
  */
@@ -251,10 +261,15 @@ static const USBEndpointConfig ep2config = {
   0x0010,
   0x0000,
   NULL,
-  NULL,
+  &ep1outstate,
   NULL
 };
 
+/**
+ * @brief   OUT EP2 state.
+ */
+USBOutEndpointState ep2outstate;
+
 /**
  * @brief   EP3 initialization structure (OUT only).
  */
@@ -266,7 +281,7 @@ static const USBEndpointConfig ep3config = {
   0x0000,
   0x0040,
   NULL,
-  NULL,
+  &ep2outstate,
   NULL
 };