diff --git a/src/libsodium/include/sodium/randombytes.h b/src/libsodium/include/sodium/randombytes.h
index d92c1a4d..08aff052 100644
--- a/src/libsodium/include/sodium/randombytes.h
+++ b/src/libsodium/include/sodium/randombytes.h
@@ -17,12 +17,12 @@ extern "C" {
 #endif
 
 typedef struct randombytes_implementation {
-    const char *(*implementation_name)(void);
-    uint32_t    (*random)(void);
-    void        (*stir)(void);
-    uint32_t    (*uniform)(const uint32_t upper_bound);
-    void        (*buf)(void * const buf, const size_t size);
-    int         (*close)(void);
+    const char *(*implementation_name)(void); /* required */
+    uint32_t    (*random)(void);              /* required */
+    void        (*stir)(void);                /* optional */
+    uint32_t    (*uniform)(const uint32_t upper_bound); /* optional, a default implementation will be used if NULL */
+    void        (*buf)(void * const buf, const size_t size); /* required */
+    int         (*close)(void);               /* optional */
 } randombytes_implementation;
 
 SODIUM_EXPORT