diff --git a/cpu/esp32/periph/hwrng.c b/cpu/esp32/periph/hwrng.c
index 9048a5ce99..c1eae7fb47 100644
--- a/cpu/esp32/periph/hwrng.c
+++ b/cpu/esp32/periph/hwrng.c
@@ -25,25 +25,15 @@
 
 #include "bootloader_random.h"
 #include "esp_random.h"
-#include "soc/wdev_reg.h"
-
-#define RNG_DATA_REG (*(volatile uint32_t *)RNG_DATA_REG_ADDR)
 
 void hwrng_init(void)
 {
-    if (!IS_USED(MODULE_WIFI_ANY)) {
-        /*
-         * The hardware RNG generates random numbers uses the noise in the
-         * RF system of the WiFi or the BT interface as entropy source.
-         * If both are disabled, the random number generator just returns
-         * pseudo-random numbers.
-         * However, the bootloader use an internal non-RF entropy source,
-         * the internal reference voltage noise. This can be re-enabled
-         * after startup as entropy source for applications that don't
-         * use the WiFi or the BT interface.
-         */
-        bootloader_random_enable();
-    }
+    /* If the ADC SAR is used, the Bootloader RNG must not be enabled before
+     * the random numbers are actually required. The reason is that the
+     * Bootloader RNG uses the noise of the ADC SAR reference voltage as
+     * a non-RF entropy source. The calibration of the ADC SAR does not
+     * work correctly in this case. Therefore, the Bootloader RNG is only
+     * enabled if random numbers are really required. */
 }
 
 /**
@@ -56,10 +46,22 @@ void hwrng_init(void)
  */
 void hwrng_read(void *buf, unsigned int num)
 {
+    if (!IS_USED(MODULE_ESP_WIFI_ANY) && !IS_USED(MODULE_ESP_BLE)) {
+        /* enable the Bootloader RNG if WiFi and BT are not used */
+        bootloader_random_enable();
+    }
+
     esp_fill_random(buf, num);
+
+    if (!IS_USED(MODULE_ESP_WIFI_ANY) && !IS_USED(MODULE_ESP_BLE)) {
+        /* disable the Bootloader RNG to ensure that ADC SAR calibration works */
+        bootloader_random_disable();
+    }
 }
 
 uint32_t hwrand(void)
 {
-    return esp_random();
+    uint32_t rand;
+    hwrng_read(&rand, 4);
+    return rand;
 }