diff --git a/po/po2json b/po/po2json
index d521f30..690d7d0 100755
--- a/po/po2json
+++ b/po/po2json
@@ -6,7 +6,7 @@ function fatal(message, code) {
 }
 
 function usage() {
-    console.log("usage: po2json [--module=template.js] input output");
+    console.log("usage: po2json [--module=template.js] [--output=output.js] input");
     process.exit(2);
 }
 
@@ -29,7 +29,7 @@ var opts = stdio.getopt({
     output: { key: "o", args: 1, description: "Output file", default: "" },
 });
 
-if (opts.args.length != 1) {
+if (!opts.args || opts.args.length != 1) {
     usage();
 }