diff --git a/ChangeLog.d/x509write_crt_set_serial_raw-alignment.txt b/ChangeLog.d/x509write_crt_set_serial_raw-alignment.txt
new file mode 100644
index 0000000000..e04f45a488
--- /dev/null
+++ b/ChangeLog.d/x509write_crt_set_serial_raw-alignment.txt
@@ -0,0 +1,3 @@
+API changes
+    * Change the serial argument of the mbedtls_x509write_crt_set_serial_raw
+      function to a const to align with the rest of the API.
diff --git a/include/mbedtls/x509_crt.h b/include/mbedtls/x509_crt.h
index bf418a6851..bbe5fc45cf 100644
--- a/include/mbedtls/x509_crt.h
+++ b/include/mbedtls/x509_crt.h
@@ -956,7 +956,7 @@ void mbedtls_x509write_crt_set_version(mbedtls_x509write_cert *ctx, int version)
  *                  is too big (longer than MBEDTLS_X509_RFC5280_MAX_SERIAL_LEN)
  */
 int mbedtls_x509write_crt_set_serial_raw(mbedtls_x509write_cert *ctx,
-                                         unsigned char *serial, size_t serial_len);
+                                         const unsigned char *serial, size_t serial_len);
 
 /**
  * \brief           Set the validity period for a Certificate
diff --git a/library/x509write_crt.c b/library/x509write_crt.c
index 1f8a006de6..663b308d62 100644
--- a/library/x509write_crt.c
+++ b/library/x509write_crt.c
@@ -94,7 +94,7 @@ int mbedtls_x509write_crt_set_issuer_name(mbedtls_x509write_cert *ctx,
 }
 
 int mbedtls_x509write_crt_set_serial_raw(mbedtls_x509write_cert *ctx,
-                                         unsigned char *serial, size_t serial_len)
+                                         const unsigned char *serial, size_t serial_len)
 {
     if (serial_len > MBEDTLS_X509_RFC5280_MAX_SERIAL_LEN) {
         return MBEDTLS_ERR_X509_BAD_INPUT_DATA;