diff --git a/lib/krb5/data.c b/lib/krb5/data.c
index d8db01569..b1efb1c36 100644
--- a/lib/krb5/data.c
+++ b/lib/krb5/data.c
@@ -78,7 +78,7 @@ krb5_data_realloc(krb5_data *p, int len)
 }
 
 krb5_error_code
-krb5_data_copy(krb5_data *p, void *data, size_t len)
+krb5_data_copy(krb5_data *p, const void *data, size_t len)
 {
     if (len) {
 	if(krb5_data_alloc(p, len))