diff --git a/io_u.c b/io_u.c
index 6567e10a5be2..33b8ac347437 100644
--- a/io_u.c
+++ b/io_u.c
@@ -1895,8 +1895,13 @@ void fill_io_buffer(struct thread_data *td, void *buf, unsigned int min_write,
 		} while (left);
 	} else if (o->buffer_pattern_bytes)
 		fill_buffer_pattern(td, buf, max_bs);
-	else
+	else if (o->zero_buffers)
 		memset(buf, 0, max_bs);
+	else {
+		struct frand_state *rs = get_buf_state(td);
+
+		fill_random_buf(rs, buf, max_bs);
+	}
 }
 
 /*