diff --git a/drivers/can.c b/drivers/can.c
index f79958bb46..dd47a2caf0 100644
--- a/drivers/can.c
+++ b/drivers/can.c
@@ -330,6 +330,7 @@ static ssize_t can_read(FAR struct file *filep, FAR char *buffer,
           do
             {
               ret = sem_wait(&dev->cd_recv.rx_sem);
+              DEBUGASSERT(ret >= 0 || errno == EINTR);
             }
           while (dev->cd_recv.rx_head == dev->cd_recv.rx_tail);
           dev->cd_nrxwaiters--;
diff --git a/include/nuttx/can.h b/include/nuttx/can.h
index dc6c2db27d..c1f59b9882 100644
--- a/include/nuttx/can.h
+++ b/include/nuttx/can.h
@@ -283,7 +283,7 @@ struct can_dev_s
 {
   uint8_t              cd_ocount;        /* The number of times the device has been opened */
   uint8_t              cd_npendrtr;      /* Number of pending RTR messages */
-  uint8_t              cd_ntxwaiters;    /* Number of threads waiting to enqueue a message */
+  volatile uint8_t     cd_ntxwaiters;    /* Number of threads waiting to enqueue a message */
   volatile uint8_t     cd_nrxwaiters;    /* Number of threads waiting to receive a message */
   sem_t                cd_closesem;      /* Locks out new opens while close is in progress */
   sem_t                cd_recvsem;       /* Used to wakeup user waiting for space in cd_recv.buffer */