diff --git a/libqpdf/MD5_native.cc b/libqpdf/MD5_native.cc
index d609c46..8cd0386 100644
--- a/libqpdf/MD5_native.cc
+++ b/libqpdf/MD5_native.cc
@@ -1,3 +1,5 @@
+// clang-format off
+
 // This file implements a class for computation of MD5 checksums.
 // It is derived from the reference algorithm for MD5 as given in
 // RFC 1321.  The original copyright notice is as follows:
diff --git a/libqpdf/rijndael.cc b/libqpdf/rijndael.cc
index c60c228..419c84f 100644
--- a/libqpdf/rijndael.cc
+++ b/libqpdf/rijndael.cc
@@ -1,3 +1,4 @@
+/* clang-format off */
 #define FULL_UNROLL
 
 #include "qpdf/rijndael.h"
diff --git a/libqpdf/sha2.c b/libqpdf/sha2.c
index b8bfaaf..cf8331f 100644
--- a/libqpdf/sha2.c
+++ b/libqpdf/sha2.c
@@ -1,3 +1,4 @@
+/* clang-format off */
 /* $Id: sha2.c 227 2010-06-16 17:28:38Z tp $ */
 /*
  * SHA-224 / SHA-256 implementation.
diff --git a/libqpdf/sha2big.c b/libqpdf/sha2big.c
index 34d1f3d..05869d3 100644
--- a/libqpdf/sha2big.c
+++ b/libqpdf/sha2big.c
@@ -1,3 +1,4 @@
+/* clang-format off */
 /* $Id: sha2big.c 216 2010-06-08 09:46:57Z tp $ */
 /*
  * SHA-384 / SHA-512 implementation.
diff --git a/libqpdf/sph/md_helper.c b/libqpdf/sph/md_helper.c
index 5c11451..2278ee9 100644
--- a/libqpdf/sph/md_helper.c
+++ b/libqpdf/sph/md_helper.c
@@ -1,3 +1,4 @@
+/* clang-format off */
 /* $Id: md_helper.c 216 2010-06-08 09:46:57Z tp $ */
 /*
  * This file contains some functions which implement the external data
diff --git a/libqpdf/sph/sph_sha2.h b/libqpdf/sph/sph_sha2.h
index dbab294..3cd929a 100644
--- a/libqpdf/sph/sph_sha2.h
+++ b/libqpdf/sph/sph_sha2.h
@@ -1,3 +1,4 @@
+/* clang-format off */
 /* $Id: sph_sha2.h 216 2010-06-08 09:46:57Z tp $ */
 /**
  * SHA-224, SHA-256, SHA-384 and SHA-512 interface.
diff --git a/libqpdf/sph/sph_types.h b/libqpdf/sph/sph_types.h
index 25beac3..df61673 100644
--- a/libqpdf/sph/sph_types.h
+++ b/libqpdf/sph/sph_types.h
@@ -1,3 +1,4 @@
+/* clang-format off */
 /* $Id: sph_types.h 260 2011-07-21 01:02:38Z tp $ */
 /**
  * Basic type definitions.