diff --git a/common/mflagext/listvar.go b/common/mflagext/listvar.go
new file mode 100644
index 0000000000..a23dc6a6b1
--- /dev/null
+++ b/common/mflagext/listvar.go
@@ -0,0 +1,31 @@
+package mflagext
+
+import (
+	"fmt"
+
+	"github.com/docker/docker/pkg/mflag"
+)
+
+type listOpts struct {
+	value      *[]string
+	hasBeenSet bool
+}
+
+func ListVar(p *[]string, names []string, value []string, usage string) {
+	*p = value
+	mflag.Var(&listOpts{p, false}, names, usage)
+}
+
+func (opts *listOpts) Set(value string) error {
+	if opts.hasBeenSet {
+		(*opts.value) = append((*opts.value), value)
+	} else {
+		(*opts.value) = []string{value}
+		opts.hasBeenSet = true
+	}
+	return nil
+}
+
+func (opts *listOpts) String() string {
+	return fmt.Sprintf("%v", []string(*opts.value))
+}
diff --git a/prog/weaveproxy/main.go b/prog/weaveproxy/main.go
index 4fe013fb89..23073b745f 100644
--- a/prog/weaveproxy/main.go
+++ b/prog/weaveproxy/main.go
@@ -7,6 +7,7 @@ import (
 
 	"github.com/docker/docker/pkg/mflag"
 	. "github.com/weaveworks/weave/common"
+	"github.com/weaveworks/weave/common/mflagext"
 	"github.com/weaveworks/weave/proxy"
 )
 
@@ -14,30 +15,6 @@ var (
 	version = "(unreleased version)"
 )
 
-type listOpts struct {
-	value      *[]string
-	hasBeenSet bool
-}
-
-func ListVar(p *[]string, names []string, value []string, usage string) {
-	*p = value
-	mflag.Var(&listOpts{p, false}, names, usage)
-}
-
-func (opts *listOpts) Set(value string) error {
-	if opts.hasBeenSet {
-		(*opts.value) = append((*opts.value), value)
-	} else {
-		(*opts.value) = []string{value}
-		opts.hasBeenSet = true
-	}
-	return nil
-}
-
-func (opts *listOpts) String() string {
-	return fmt.Sprintf("%v", []string(*opts.value))
-}
-
 func main() {
 	var (
 		justVersion bool
@@ -49,7 +26,7 @@ func main() {
 
 	mflag.BoolVar(&justVersion, []string{"#version", "-version"}, false, "print version and exit")
 	mflag.StringVar(&logLevel, []string{"-log-level"}, "info", "logging level (debug, info, warning, error)")
-	ListVar(&c.ListenAddrs, []string{"H"}, nil, "addresses on which to listen")
+	mflagext.ListVar(&c.ListenAddrs, []string{"H"}, nil, "addresses on which to listen")
 	mflag.StringVar(&c.HostnameMatch, []string{"-hostname-match"}, "(.*)", "Regexp pattern to apply on container names (e.g. '^aws-[0-9]+-(.*)$')")
 	mflag.StringVar(&c.HostnameReplacement, []string{"-hostname-replacement"}, "$1", "Expression to generate hostnames based on matches from --hostname-match (e.g. 'my-app-$1')")
 	mflag.BoolVar(&c.NoDefaultIPAM, []string{"#-no-default-ipam", "-no-default-ipalloc"}, false, "do not automatically allocate addresses for containers without a WEAVE_CIDR")