diff --git a/unix/pterm.c b/unix/pterm.c
index a7c2f735..692c704f 100644
--- a/unix/pterm.c
+++ b/unix/pterm.c
@@ -1732,6 +1732,9 @@ int do_cmdline(int argc, char **argv, int do_everything)
 	    EXPECTS_ARG;
 	    provide_xrm_string(val);
 
+	} else {
+	    err = 1;
+	    fprintf(stderr, "pterm: unrecognized option '%s'\n", p);
 	}
     }