diff --git a/demos/openssl-enc.c b/demos/openssl-enc.c
index 2112101..3aca04f 100644
--- a/demos/openssl-enc.c
+++ b/demos/openssl-enc.c
@@ -89,7 +89,7 @@ union paddable {
  * Output:       <no return>
  * Side Effects: print messages and barf (does exit(3))
  */
-void barf(char *pname, char *err)
+void barf(const char *pname, const char *err)
 {
    printf("Usage: %s <enc|dec> infile outfile passphrase [salt]\n", pname);
    printf("\n");