Wrap <stdint.h> in #ifdef HAVE_STDINT_H.
diff --git a/xmss_fast.c b/xmss_fast.c
index 6aff36a..b918f13 100644
--- a/xmss_fast.c
+++ b/xmss_fast.c
@@ -10,7 +10,9 @@
 #include "xmss_fast.h"
 #include <stdlib.h>
 #include <string.h>
+#ifdef HAVE_STDINT_H
 #include <stdint.h>
+#endif
 
 #include "crypto_api.h"
 #include "xmss_wots.h"