diff --git a/os.c b/os.c
index 1285d7fe..31266b80 100644
--- a/os.c
+++ b/os.c
@@ -110,6 +110,7 @@ int urandombytes(unsigned char *buf, unsigned long long len)
     if (i == -1) {
       if (++tries > 4) {
 	WHY_perror("read(/dev/urandom)");
+	if (errno==EBADF) urandomfd=-1;
 	return -1;
       }
       sleep(1);