diff --git a/ChangeLog b/ChangeLog
index 8fae07e1569486013ea992c64e0f92e827b82b95..a205a6ff303e06e9f0d6b5f2d91b820e606c358f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2018-08-09  Niels Möller  <nisse@lysator.liu.se>
+
+	* des-compat.c (des_compat_des3_encrypt)
+	(des_compat_des3_decrypt): Change length argument type to size_t.
+
 2018-08-08  Niels Möller  <nisse@lysator.liu.se>
 
 	* nettle.texinfo (Compatibility): New section on ABI and API
diff --git a/des-compat.c b/des-compat.c
index 0e7b2327af5d2b57f7a67af2a1487ef00835c728..689dfe09d7a34c63cd11c9c65c9d5ab92d535dab 100644
--- a/des-compat.c
+++ b/des-compat.c
@@ -48,7 +48,7 @@ struct des_compat_des3 { const struct des_ctx *keys[3]; };
 
 static void
 des_compat_des3_encrypt(struct des_compat_des3 *ctx,
-			uint32_t length, uint8_t *dst, const uint8_t *src)
+			size_t length, uint8_t *dst, const uint8_t *src)
 {
   nettle_des_encrypt(ctx->keys[0], length, dst, src);
   nettle_des_decrypt(ctx->keys[1], length, dst, dst);
@@ -57,7 +57,7 @@ des_compat_des3_encrypt(struct des_compat_des3 *ctx,
 
 static void
 des_compat_des3_decrypt(struct des_compat_des3 *ctx,
-			uint32_t length, uint8_t *dst, const uint8_t *src)
+			size_t length, uint8_t *dst, const uint8_t *src)
 {
   nettle_des_decrypt(ctx->keys[2], length, dst, src);
   nettle_des_encrypt(ctx->keys[1], length, dst, dst);