diff --git a/crypto/x509/x509type.c b/crypto/x509/x509type.c
index 8c7242cc6626ed7a3835a14cf2e6c61b3add0cda..aca8355273309d301b57ed1944842698925f1eb9 100644
--- a/crypto/x509/x509type.c
+++ b/crypto/x509/x509type.c
@@ -13,7 +13,7 @@
 #include <openssl/objects.h>
 #include <openssl/x509.h>
 
-int X509_certificate_type(X509 *x, const EVP_PKEY *pkey)
+int X509_certificate_type(const X509 *x, const EVP_PKEY *pkey)
 {
     const EVP_PKEY *pk;
     int ret = 0, i;
diff --git a/include/openssl/x509.h b/include/openssl/x509.h
index fc23d9b91b4b11e97ae532bcd817c8d023fa9522..22385295e3c781fe15be00f5f9fc09aebb1ae711 100644
--- a/include/openssl/x509.h
+++ b/include/openssl/x509.h
@@ -639,7 +639,7 @@ const X509_ALGOR *X509_get0_tbs_sigalg(const X509 *x);
 EVP_PKEY *X509_get0_pubkey(const X509 *x);
 EVP_PKEY *X509_get_pubkey(X509 *x);
 ASN1_BIT_STRING *X509_get0_pubkey_bitstr(const X509 *x);
-int X509_certificate_type(X509 *x, const EVP_PKEY *pubkey /* optional */ );
+int X509_certificate_type(const X509 *x, const EVP_PKEY *pubkey);
 
 long X509_REQ_get_version(const X509_REQ *req);
 int X509_REQ_set_version(X509_REQ *x, long version);