diff --git a/libqpdf/qpdf/QPDFCrypto_gnutls.hh b/libqpdf/qpdf/QPDFCrypto_gnutls.hh
index f17c447..18945cb 100644
--- a/libqpdf/qpdf/QPDFCrypto_gnutls.hh
+++ b/libqpdf/qpdf/QPDFCrypto_gnutls.hh
@@ -4,7 +4,11 @@
 #include <qpdf/DLL.h>
 #include <qpdf/QPDFCryptoImpl.hh>
 #include <memory>
+
+// gnutls headers must be last to prevent them from interfering with
+// other headers. gnutls.h has to be included first.
 #include <gnutls/gnutls.h>
+// This comment prevents clang-format from putting crypto.h before gnutls.h
 #include <gnutls/crypto.h>
 
 class QPDFCrypto_gnutls: public QPDFCryptoImpl