diff --git a/drivers/entropy/Kconfig.nrf5 b/drivers/entropy/Kconfig.nrf5
index 9d1273163be..b02a49ffaee 100644
--- a/drivers/entropy/Kconfig.nrf5
+++ b/drivers/entropy/Kconfig.nrf5
@@ -25,8 +25,17 @@ config ENTROPY_NRF5_BIAS_CORRECTION
 	  uniform distribution of 0 and 1. When this option is enabled, the time
 	  to generate a byte cannot be guaranteed.
 
+config ENTROPY_NRF5_THR_POOL_SIZE
+	int "Thread-mode random number pool size"
+	range ENTROPY_NRF5_THR_THRESHOLD 256
+	default 8
+	help
+	  Buffer length in bytes used to store entropy bytes generated by the
+	  hardware to make them ready for thread mode consumers.
+	  Please note, that size of the pool must be a power of 2.
+
 config ENTROPY_NRF5_THR_THRESHOLD
-	int "Thread-mode low-water threshold"
+	int "Thread-mode random number pool low-water threshold"
 	range 4 255
 	help
 	  Low water-mark threshold in bytes to trigger entropy generation for
@@ -34,8 +43,17 @@ config ENTROPY_NRF5_THR_THRESHOLD
 	  buffer goes below this number hardware entropy generation will be
 	  started.
 
+config ENTROPY_NRF5_ISR_POOL_SIZE
+	int "ISR-mode random number pool size"
+	range ENTROPY_NRF5_ISR_THRESHOLD 256
+	default 16
+	help
+	  Buffer length in bytes used to store entropy bytes generated by the
+	  hardware to make them ready for ISR consumers.
+	  Please note, that size of the pool must be a power of 2.
+
 config ENTROPY_NRF5_ISR_THRESHOLD
-	int "ISR low-water threshold"
+	int "ISR-mode random number pool low-water threshold"
 	range 12 255
 	help
 	  Low water-mark threshold in bytes to trigger entropy generation for
@@ -43,19 +61,6 @@ config ENTROPY_NRF5_ISR_THRESHOLD
 	  buffer goes below this number hardware entropy generation will be
 	  started.
 
-config ENTROPY_NRF5_THR_BUF_LEN
-	int "Thread-mode buffer length"
-	range ENTROPY_NRF5_THR_THRESHOLD 255
-	help
-	  Buffer length in bytes used to store entropy bytes generated by the
-	  hardware to make them ready for thread mode consumers.
-
-config ENTROPY_NRF5_ISR_BUF_LEN
-	int "ISR buffer length"
-	range ENTROPY_NRF5_ISR_THRESHOLD 255
-	help
-	  Buffer length in bytes used to store entropy bytes generated by the
-	  hardware to make them ready for ISR consumers.
 
 config ENTROPY_NRF5_PRI
 	int "RNG interrupt priority"
diff --git a/drivers/entropy/entropy_nrf5.c b/drivers/entropy/entropy_nrf5.c
index 32341349f43..2d15ae06aa3 100644
--- a/drivers/entropy/entropy_nrf5.c
+++ b/drivers/entropy/entropy_nrf5.c
@@ -64,24 +64,30 @@
  */
 
 struct rng_pool {
-	u8_t count;
-	u8_t threshold;
-	u8_t first;
+	u8_t first_alloc;
+	u8_t first_read;
 	u8_t last;
-	u8_t rand[0];
+	u8_t mask;
+	u8_t threshold;
+	u8_t buffer[0];
 };
 
-#define RNG_POOL_DEFINE(name, len) u8_t name[sizeof(struct rng_pool) + len] __aligned(4)
+#define RNG_POOL_DEFINE(name, len) u8_t name[sizeof(struct rng_pool) + (len)]
 
-#define RNG_POOL_ISR_LEN (CONFIG_ENTROPY_NRF5_ISR_BUF_LEN + 1)
-#define RNG_POOL_THR_LEN (CONFIG_ENTROPY_NRF5_THR_BUF_LEN + 1)
+BUILD_ASSERT_MSG((CONFIG_ENTROPY_NRF5_ISR_POOL_SIZE &
+		 (CONFIG_ENTROPY_NRF5_ISR_POOL_SIZE - 1)) == 0,
+		 "The CONFIG_ENTROPY_NRF5_ISR_POOL_SIZE must be a power of 2!");
+
+BUILD_ASSERT_MSG((CONFIG_ENTROPY_NRF5_THR_POOL_SIZE &
+		 (CONFIG_ENTROPY_NRF5_THR_POOL_SIZE - 1)) == 0,
+		 "The CONFIG_ENTROPY_NRF5_THR_POOL_SIZE must be a power of 2!");
 
 struct entropy_nrf5_dev_data {
 	struct k_sem sem_lock;
 	struct k_sem sem_sync;
 
-	RNG_POOL_DEFINE(isr, RNG_POOL_ISR_LEN);
-	RNG_POOL_DEFINE(thr, RNG_POOL_THR_LEN);
+	RNG_POOL_DEFINE(isr, CONFIG_ENTROPY_NRF5_ISR_POOL_SIZE);
+	RNG_POOL_DEFINE(thr, CONFIG_ENTROPY_NRF5_THR_POOL_SIZE);
 };
 
 #define DEV_DATA(dev) \
@@ -108,121 +114,87 @@ static int random_byte_get(void)
 #if defined(CONFIG_BT_CTLR_FAST_ENC)
 #pragma GCC optimize ("Ofast")
 #endif
-static inline u8_t rng_pool_get(struct rng_pool *rng, u8_t octets, u8_t *rand)
+static u16_t rng_pool_get(struct rng_pool *rngp, u8_t *buf, u16_t len)
 {
-	u8_t first, last, avail, remaining, *d, *s;
+	u32_t last  = rngp->last;
+	u32_t mask  = rngp->mask;
+	u8_t *dst   = buf;
+	u32_t first, available;
+	u32_t other_read_in_progress;
+	unsigned int key;
 
-	__ASSERT_NO_MSG(rng);
+	key = irq_lock();
+	first = rngp->first_alloc;
 
-	first = rng->first;
-	last = rng->last;
+	/*
+	 * The other_read_in_progress is non-zero if rngp->first_read != first,
+	 * which means that lower-priority code (which was interrupted by this
+	 * call) already allocated area for read.
+	 */
+	other_read_in_progress = (rngp->first_read ^ first);
 
-	d = &rand[octets];
-	s = &rng->rand[first];
-
-	if (first <= last) {
-		/* copy octets from contiguous memory */
-		avail = last - first;
-		if (octets < avail) {
-			remaining = avail - octets;
-			avail = octets;
-		} else {
-			remaining = 0;
-		}
-
-		first += avail;
-		octets -= avail;
-
-		while (avail--) {
-			*(--d) = *s++;
-		}
-
-		rng->first = first;
-	} else {
-		/* copy octets from split halves - until end of array */
-		avail = rng->count - first;
-		if (octets < avail) {
-			remaining = avail + last - octets;
-			avail = octets;
-			first += avail;
-		} else {
-			remaining = last;
-			first = 0;
-		}
-
-		octets -= avail;
-
-		while (avail--) {
-			*(--d) = *s++;
-		}
-
-		/* copy from beginning of array - until ring buffer last idx */
-		if (octets && last) {
-			s = &rng->rand[0];
-
-			if (octets < last) {
-				remaining = last - octets;
-				last = octets;
-			} else {
-				remaining = 0;
-			}
-
-			first = last;
-			octets -= last;
-
-			while (last--) {
-				*(--d) = *s++;
-			}
-		}
-
-		rng->first = first;
+	available = (last - first) & mask;
+	if (available < len) {
+		len = available;
 	}
 
-	if (remaining < rng->threshold) {
+	/*
+	 * Move alloc index forward to signal, that part of the buffer is
+	 * now reserved for this call.
+	 */
+	rngp->first_alloc = (first + len) & mask;
+	irq_unlock(key);
+
+	while (likely(len--)) {
+		*dst++ = rngp->buffer[first];
+		first = (first + 1) & mask;
+	}
+
+	/*
+	 * If this call is the last one accessing the pool, move read index
+	 * to signal that all allocated regions are now read and could be
+	 * overwritten.
+	 */
+	if (likely(!other_read_in_progress)) {
+		key = irq_lock();
+		rngp->first_read = rngp->first_alloc;
+		irq_unlock(key);
+	}
+
+	len = dst - buf;
+	available = available - len;
+	if (available <= rngp->threshold) {
 		nrf_rng_task_trigger(NRF_RNG_TASK_START);
 	}
 
-	return octets;
+	return len;
 }
 #pragma GCC pop_options
 
-static int rng_pool_put(struct rng_pool *rng, bool store, u8_t byte)
+static int rng_pool_put(struct rng_pool *rngp, u8_t byte)
 {
-	u8_t last;
+	u8_t first = rngp->first_read;
+	u8_t last  = rngp->last;
+	u8_t mask  = rngp->mask;
 
-	if (!rng) {
+	/* Signal error if the pool is full. */
+	if (((last - first) & mask) == mask) {
 		return -ENOBUFS;
 	}
 
-	last = rng->last + 1;
-	if (last == rng->count) {
-		last = 0;
-	}
+	rngp->buffer[last] = byte;
+	rngp->last = (last + 1) & mask;
 
-	if (last == rng->first) {
-		/* this condition should not happen, but due to probable race,
-		 * new value could be generated before NRF_RNG task is stopped.
-		 */
-		return -ENOBUFS;
-	}
+	return 0;
+}
 
-	if (!store) {
-		return -EBUSY;
-	}
-
-	rng->rand[rng->last] = byte;
-	rng->last = last;
-
-	last = rng->last + 1;
-	if (last == rng->count) {
-		last = 0;
-	}
-
-	if (last == rng->first) {
-		return 0;
-	}
-
-	return -EBUSY;
+static void rng_pool_init(struct rng_pool *rngp, u16_t size, u8_t threshold)
+{
+	rngp->first_alloc = 0;
+	rngp->first_read  = 0;
+	rngp->last	  = 0;
+	rngp->mask	  = size - 1;
+	rngp->threshold	  = threshold;
 }
 
 static void isr(void *arg)
@@ -235,23 +207,15 @@ static void isr(void *arg)
 		return;
 	}
 
-	ret = rng_pool_put((struct rng_pool *)dev_data->isr, true, byte);
-	if (ret != -EBUSY) {
-		ret = rng_pool_put((struct rng_pool *)dev_data->thr,
-			           (ret == -ENOBUFS), byte);
+	ret = rng_pool_put((struct rng_pool *)dev_data->isr, byte);
+	if (ret < 0) {
+		ret = rng_pool_put((struct rng_pool *)dev_data->thr, byte);
+		if (ret < 0) {
+			nrf_rng_task_trigger(NRF_RNG_TASK_STOP);
+		}
+
 		k_sem_give(&dev_data->sem_sync);
 	}
-
-	if (ret != -EBUSY) {
-		nrf_rng_task_trigger(NRF_RNG_TASK_STOP);
-	}
-}
-
-static void rng_pool_init(struct rng_pool *rng, u8_t len, u8_t threshold)
-{
-	rng->count = len;
-	rng->threshold = threshold;
-	rng->first = rng->last = 0;
 }
 
 static int entropy_nrf5_get_entropy(struct device *device, u8_t *buf, u16_t len)
@@ -259,25 +223,21 @@ static int entropy_nrf5_get_entropy(struct device *device, u8_t *buf, u16_t len)
 	struct entropy_nrf5_dev_data *dev_data = DEV_DATA(device);
 
 	while (len) {
-		u8_t len8;
+		u16_t bytes;
 
-		if (len > UINT8_MAX) {
-			len8 = UINT8_MAX;
-		} else {
-			len8 = len;
-		}
-		len -= len8;
+		k_sem_take(&dev_data->sem_lock, K_FOREVER);
+		bytes = rng_pool_get((struct rng_pool *)dev_data->thr,
+				     buf, len);
+		k_sem_give(&dev_data->sem_lock);
 
-		while (len8) {
-			k_sem_take(&dev_data->sem_lock, K_FOREVER);
-			len8 = rng_pool_get((struct rng_pool *)dev_data->thr,
-					    len8, buf);
-			k_sem_give(&dev_data->sem_lock);
-			if (len8) {
-				/* Sleep until next interrupt */
-				k_sem_take(&dev_data->sem_sync, K_FOREVER);
-			}
+		if (bytes == 0) {
+			/* Pool is empty: Sleep until next interrupt. */
+			k_sem_take(&dev_data->sem_sync, K_FOREVER);
+			continue;
 		}
+
+		len -= bytes;
+		buf += bytes;
 	}
 
 	return 0;
@@ -290,7 +250,7 @@ static int entropy_nrf5_get_entropy_isr(struct device *dev, u8_t *buf, u16_t len
 	u16_t cnt = len;
 
 	if (!(flags & ENTROPY_BUSYWAIT)) {
-		return rng_pool_get((struct rng_pool *)dev_data->isr, len, buf);
+		return rng_pool_get((struct rng_pool *)dev_data->isr, buf, len);
 	}
 
 	if (len) {
@@ -351,13 +311,16 @@ static int entropy_nrf5_init(struct device *device)
 
 	/* Locking semaphore initialized to 1 (unlocked) */
 	k_sem_init(&dev_data->sem_lock, 1, 1);
+
 	/* Synching semaphore */
 	k_sem_init(&dev_data->sem_sync, 0, 1);
 
-	rng_pool_init((struct rng_pool *)dev_data->thr, RNG_POOL_THR_LEN,
-	              CONFIG_ENTROPY_NRF5_THR_THRESHOLD);
-	rng_pool_init((struct rng_pool *)dev_data->isr, RNG_POOL_ISR_LEN,
-	              CONFIG_ENTROPY_NRF5_ISR_THRESHOLD);
+	rng_pool_init((struct rng_pool *)dev_data->thr,
+		      CONFIG_ENTROPY_NRF5_THR_POOL_SIZE,
+		      CONFIG_ENTROPY_NRF5_THR_THRESHOLD);
+	rng_pool_init((struct rng_pool *)dev_data->isr,
+		      CONFIG_ENTROPY_NRF5_ISR_POOL_SIZE,
+		      CONFIG_ENTROPY_NRF5_ISR_THRESHOLD);
 
 	/* Enable or disable bias correction */
 	if (IS_ENABLED(CONFIG_ENTROPY_NRF5_BIAS_CORRECTION)) {
@@ -380,6 +343,6 @@ static int entropy_nrf5_init(struct device *device)
 u8_t entropy_nrf_get_entropy_isr(struct device *dev, u8_t *buf, u8_t len)
 {
 	ARG_UNUSED(dev);
-	return rng_pool_get((struct rng_pool *)entropy_nrf5_data.isr, len, buf);
+	return rng_pool_get((struct rng_pool *)entropy_nrf5_data.isr, buf, len);
 }