diff --git a/libqpdf/qpdf/rijndael.h b/libqpdf/qpdf/rijndael.h
index 57fa2027..0c04ba54 100644
--- a/libqpdf/qpdf/rijndael.h
+++ b/libqpdf/qpdf/rijndael.h
@@ -2,13 +2,8 @@
 #define RIJNDAEL_H
 
 #include <qpdf/qpdf-config.h>
-#ifdef HAVE_INTTYPES_H
-# include <inttypes.h>
-#endif
-#ifdef HAVE_STDINT_H
-# include <stdint.h>
-#endif
-#include <stddef.h>
+#include <cstdint>
+#include <cstddef>
 
 unsigned int rijndaelSetupEncrypt(uint32_t* rk, const unsigned char* key, size_t keybits);
 unsigned int rijndaelSetupDecrypt(uint32_t* rk, const unsigned char* key, size_t keybits);