diff --git a/sys/include/random.h b/sys/include/random.h
index 317caa8bc4..56baa9f7a6 100644
--- a/sys/include/random.h
+++ b/sys/include/random.h
@@ -21,6 +21,11 @@
  *    HWRNG differ in how they generate random numbers and may not use a PRNG internally.
  *    Refer to the manual of your MCU for details.
  *
+ * By default, the `auto_init_random` module is enabled, which initializes the
+ * PRNG on startup. However, there is no lower limit on the entropy provided at
+ * that time. Unless the `periph_hwrng` module is used, entropy may be as
+ * little as zero (the constant may even be the same across devices).
+ *
  * @{
  *
  * @file
@@ -55,6 +60,9 @@ extern "C" {
 /**
  * @brief initializes PRNG with a seed
  *
+ * Users only need to call this if the `auto_init_random` module is disabled,
+ * or provides insufficient quality entropy.
+ *
  * @warning Currently, the random module uses a global state
  * => multiple calls to @ref random_init will reset the existing
  * state of the PRNG.