diff --git a/main.go b/main.go
index f81a25e..1b3677e 100644
--- a/main.go
+++ b/main.go
@@ -5,16 +5,10 @@ import (
 	_ "embed"
 	"flag"
 	"fmt"
-	"io/ioutil"
 	"log"
 	"os"
-	"path/filepath"
 	"os/signal"
 
-	"golang.org/x/mod/modfile"
-	"golang.org/x/mod/module"
-	"golang.org/x/mod/zip"
-
 	"orel.li/modularium/internal/index"
 	"orel.li/modularium/internal/ref"
 )
@@ -71,51 +65,6 @@ func serve(args []string) {
 	}
 }
 
-func zipcmd(args []string) {
-	var (
-		version string
-		outputPath string
-	)
-
-	flags := flag.NewFlagSet("zip", flag.ExitOnError)
-	flags.StringVar(&version, "version", "", "package version")
-	flags.StringVar(&outputPath, "o", "a.zip", "output file path")
-	flags.Parse(args)
-	if version == "" {
-		bail(1, "target release version is required")
-	}
-
-	pkgdir := flags.Arg(0)
-	modfilePath := filepath.Join(pkgdir, "go.mod")
-	b, err := ioutil.ReadFile(modfilePath)
-	if err != nil {
-		bail(1, "unable to read modfile: %v", err)
-	}
-
-	log_info.Printf("checking modfile at path %q", modfilePath)
-	f, err := modfile.Parse(modfilePath, b, nil)
-	if err != nil {
-		bail(1, "unable to parse modfile: %v", err)
-	}
-	modpath := f.Module.Mod.Path
-	log_info.Print("parsed modfile")
-	log_info.Printf("module path in modfile: %s", modpath)
-	log_info.Printf("module major version in modfile: %s", f.Module.Mod.Version)
-	log_info.Printf("target release version: %s", version)
-	if err := module.Check(modpath, version); err != nil {
-		shutdown(err)
-	}
-	zf, err := os.OpenFile(outputPath, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0644)
-	if err != nil {
-		bail(1, "output file not opened: %v", err)
-	}
-
-	mv := module.Version{Path: modpath, Version: version}
-	if err := zip.CreateFromDir(zf, mv, pkgdir); err != nil {
-		bail(1, "zip not created: %v", err)
-	}
-}
-
 func main() {
 	sigCancel(context.Background())
 	root := flag.NewFlagSet("", flag.ExitOnError)
diff --git a/zip.go b/zip.go
new file mode 100644
index 0000000..04fdaf4
--- /dev/null
+++ b/zip.go
@@ -0,0 +1,57 @@
+package main
+
+import (
+	"flag"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	"golang.org/x/mod/modfile"
+	"golang.org/x/mod/module"
+	"golang.org/x/mod/zip"
+)
+
+func zipcmd(args []string) {
+	var (
+		version    string
+		outputPath string
+	)
+
+	flags := flag.NewFlagSet("zip", flag.ExitOnError)
+	flags.StringVar(&version, "version", "", "package version")
+	flags.StringVar(&outputPath, "o", "a.zip", "output file path")
+	flags.Parse(args)
+	if version == "" {
+		bail(1, "target release version is required")
+	}
+
+	pkgdir := flags.Arg(0)
+	modfilePath := filepath.Join(pkgdir, "go.mod")
+	b, err := ioutil.ReadFile(modfilePath)
+	if err != nil {
+		bail(1, "unable to read modfile: %v", err)
+	}
+
+	log_info.Printf("checking modfile at path %q", modfilePath)
+	f, err := modfile.Parse(modfilePath, b, nil)
+	if err != nil {
+		bail(1, "unable to parse modfile: %v", err)
+	}
+	modpath := f.Module.Mod.Path
+	log_info.Print("parsed modfile")
+	log_info.Printf("module path in modfile: %s", modpath)
+	log_info.Printf("module major version in modfile: %s", f.Module.Mod.Version)
+	log_info.Printf("target release version: %s", version)
+	if err := module.Check(modpath, version); err != nil {
+		shutdown(err)
+	}
+	zf, err := os.OpenFile(outputPath, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0644)
+	if err != nil {
+		bail(1, "output file not opened: %v", err)
+	}
+
+	mv := module.Version{Path: modpath, Version: version}
+	if err := zip.CreateFromDir(zf, mv, pkgdir); err != nil {
+		bail(1, "zip not created: %v", err)
+	}
+}