diff --git a/boost/uuid/seed_rng.hpp b/boost/uuid/seed_rng.hpp
index 3090197..4196536 100644
--- a/boost/uuid/seed_rng.hpp
+++ b/boost/uuid/seed_rng.hpp
@@ -150,7 +150,8 @@ private:
 
             if(random_)
             {
-                std::fread( buffer, 1, 20, random_ );
+                size_t rnd_read_size = std::fread( buffer, 1, sizeof(buffer), random_ );
+                BOOST_ASSERT(rnd_read_size == sizeof(buffer));
             }
 
             // using an uninitialized buffer[] if fopen fails