diff --git a/context.c b/context.c

index 8b3754b..9128a82 100644

--- a/context.c

+++ b/context.c

@@ -83,9 +83,12 @@ auth_fn (SMBCCTX *ctx,

       return;

     }

-  strncpy (workgroup, use_workgroup, wgmaxlen);

-  strncpy (username, use_username, unmaxlen);

-  strncpy (password, use_password, pwmaxlen);

+  strncpy (workgroup, use_workgroup, wgmaxlen - 1);

+  workgroup[wgmaxlen - 1] = '\0';

+  strncpy (username, use_username, unmaxlen - 1);

+  username[unmaxlen - 1] = '\0';

+  strncpy (password, use_password, pwmaxlen - 1);

+  password[pwmaxlen - 1] = '\0';

   Py_DECREF (result);

   debugprintf ("<- auth_fn(), got callback result\n");

 }