Wrap <stdint.h> in #ifdef HAVE_STDINT_H.
diff --git a/xmss_hash.c b/xmss_hash.c
index 9c42c4f..c4cac47 100644
--- a/xmss_hash.c
+++ b/xmss_hash.c
@@ -12,7 +12,9 @@
 #include "xmss_hash.h"
 
 #include <stddef.h>
+#ifdef HAVE_STDINT_H
 #include <stdint.h>
+#endif
 #include <stdio.h>
 #include <string.h>
 #include <openssl/sha.h>