diff --git a/ChangeLog b/ChangeLog
index 196a946ce43840e8d9e3ca668d282279dae66ae6..910b696d60764405d6a3dc38794ca7d2acb80a6c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2019-12-04  Niels Möller  <nisse@lysator.liu.se>
+
+	* testsuite/testutils.c (test_cipher_cfb8): Add cast of size_t to
+	unsigned long for argument to fprintf.
+
 2019-11-21  Niels Möller  <nisse@lysator.liu.se>
 
 	* eccdata.c (ecc_curve_init_str): Delete unused t and d arguments.
diff --git a/testsuite/testutils.c b/testsuite/testutils.c
index c9f21bab23462e447e0613c7184ac20c344cf14f..208d413c82bb4a5d7aa768e15037991840bf3a64 100644
--- a/testsuite/testutils.c
+++ b/testsuite/testutils.c
@@ -466,7 +466,7 @@ test_cipher_cfb8(const struct nettle_cipher *cipher,
       if (!MEMEQ(length, data, ciphertext->data))
 	{
 	  fprintf(stderr, "CFB8 encrypt failed, block size %lu:\nInput:",
-		  block);
+		  (unsigned long) block);
 	  tstring_print_hex(cleartext);
 	  fprintf(stderr, "\nOutput: ");
 	  print_hex(length, data);
@@ -494,7 +494,7 @@ test_cipher_cfb8(const struct nettle_cipher *cipher,
       if (!MEMEQ(length, data2, cleartext->data))
 	{
 	  fprintf(stderr, "CFB8 decrypt failed, block size %lu:\nInput:",
-		  block);
+		  (unsigned long) block);
 	  tstring_print_hex(ciphertext);
 	  fprintf(stderr, "\nOutput: ");
 	  print_hex(length, data2);