diff --git a/src/random.h b/src/random.h
index 0e8bb2717..29de58731 100644
--- a/src/random.h
+++ b/src/random.h
@@ -46,7 +46,11 @@ public:
     uint32_t Rw;
 };
 
-/* Number of random bytes returned by GetOSRand */
+/* Number of random bytes returned by GetOSRand.
+ * When changing this constant make sure to change all call sites, and make
+ * sure that the underlying OS APIs for all platforms support the number.
+ * (many cap out at 256 bytes).
+ */
 static const ssize_t NUM_OS_RANDOM_BYTES = 32;
 
 /** Get 32 bytes of system entropy. Do not use this in application code: use