diff --git a/crypto/x509/x509_lcl.h b/crypto/x509/x509_lcl.h
index 0ef5bc3764..9b22974f4d 100644
--- a/crypto/x509/x509_lcl.h
+++ b/crypto/x509/x509_lcl.h
@@ -80,10 +80,10 @@ struct x509_lookup_method_st {
                                  X509_NAME *name, ASN1_INTEGER *serial,
                                  X509_OBJECT *ret);
     int (*get_by_fingerprint) (X509_LOOKUP *ctx, X509_LOOKUP_TYPE type,
-                               unsigned char *bytes, int len,
+                               const unsigned char *bytes, int len,
                                X509_OBJECT *ret);
     int (*get_by_alias) (X509_LOOKUP *ctx, X509_LOOKUP_TYPE type,
-                         char *str, int len, X509_OBJECT *ret);
+                         const char *str, int len, X509_OBJECT *ret);
 };
 
 /* This is the functions plus an instance of the local variables. */
diff --git a/crypto/x509/x509_lu.c b/crypto/x509/x509_lu.c
index 79c68fedfc..952cbfb329 100644
--- a/crypto/x509/x509_lu.c
+++ b/crypto/x509/x509_lu.c
@@ -101,7 +101,7 @@ int X509_LOOKUP_by_issuer_serial(X509_LOOKUP *ctx, X509_LOOKUP_TYPE type,
 }
 
 int X509_LOOKUP_by_fingerprint(X509_LOOKUP *ctx, X509_LOOKUP_TYPE type,
-                               unsigned char *bytes, int len,
+                               const unsigned char *bytes, int len,
                                X509_OBJECT *ret)
 {
     if ((ctx->method == NULL) || (ctx->method->get_by_fingerprint == NULL))
@@ -110,7 +110,7 @@ int X509_LOOKUP_by_fingerprint(X509_LOOKUP *ctx, X509_LOOKUP_TYPE type,
 }
 
 int X509_LOOKUP_by_alias(X509_LOOKUP *ctx, X509_LOOKUP_TYPE type,
-                         char *str, int len, X509_OBJECT *ret)
+                         const char *str, int len, X509_OBJECT *ret)
 {
     if ((ctx->method == NULL) || (ctx->method->get_by_alias == NULL))
         return 0;
diff --git a/include/openssl/x509_vfy.h b/include/openssl/x509_vfy.h
index a0f79276be..a5c9b4ad83 100644
--- a/include/openssl/x509_vfy.h
+++ b/include/openssl/x509_vfy.h
@@ -387,10 +387,10 @@ int X509_LOOKUP_by_issuer_serial(X509_LOOKUP *ctx, X509_LOOKUP_TYPE type,
                                  X509_NAME *name, ASN1_INTEGER *serial,
                                  X509_OBJECT *ret);
 int X509_LOOKUP_by_fingerprint(X509_LOOKUP *ctx, X509_LOOKUP_TYPE type,
-                               unsigned char *bytes, int len,
+                               const unsigned char *bytes, int len,
                                X509_OBJECT *ret);
 int X509_LOOKUP_by_alias(X509_LOOKUP *ctx, X509_LOOKUP_TYPE type,
-                         char *str, int len, X509_OBJECT *ret);
+                         const char *str, int len, X509_OBJECT *ret);
 int X509_LOOKUP_shutdown(X509_LOOKUP *ctx);
 
 int X509_STORE_load_locations(X509_STORE *ctx,