diff --git a/README.md b/README.md
index 952ed4f..b081a09 100644
--- a/README.md
+++ b/README.md
@@ -41,8 +41,15 @@ document.
 
 This can be achieved with a number of methods.
 
+The simplest method is to tell `packserver` itself which resource to use
+instead of returning an HTTP 404. Use the command line argument
+`--fallback-404 /index.html` (or whichever named resource). The filename must
+match a packed resource, so it will be preceded with a `/`. It must exist in
+all packfiles being served.
+
 If you have an nginx instance reverse proxying in front of `htpack`, then you
-can use a couple of extra directives, for example:
+can use a couple of extra directives. This is very flexible as it lets you
+override the resource for different routes. For example:
 
 	# prevent page loaded at "http://server.example/my-application" from
 	# requesting resources at "/*" when it should request them at
diff --git a/cmd/packserver/go.mod b/cmd/packserver/go.mod
index 06f2135..c9ade42 100644
--- a/cmd/packserver/go.mod
+++ b/cmd/packserver/go.mod
@@ -4,5 +4,5 @@ go 1.13
 
 require (
 	github.com/spf13/cobra v0.0.5
-	src.lwithers.me.uk/go/htpack v1.1.5
+	src.lwithers.me.uk/go/htpack v1.2.0
 )
diff --git a/cmd/packserver/go.sum b/cmd/packserver/go.sum
index 9c25300..caf2172 100644
--- a/cmd/packserver/go.sum
+++ b/cmd/packserver/go.sum
@@ -38,5 +38,5 @@ golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/tools v0.0.0-20180221164845-07fd8470d635/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
-src.lwithers.me.uk/go/htpack v1.1.5 h1:2JzgqLZ1ROYc53+96NezfJ3S9fkwHZNd6QgJhMXnlSE=
-src.lwithers.me.uk/go/htpack v1.1.5/go.mod h1:JWofpm01RJbCTIyKfIPftUsxk6KlFkrYwyHgCVdKY+s=
+src.lwithers.me.uk/go/htpack v1.2.0 h1:z0bI8KalSD5kPYOcnuqZRPun80Ww0wbnjMkYYuv+xAI=
+src.lwithers.me.uk/go/htpack v1.2.0/go.mod h1:JWofpm01RJbCTIyKfIPftUsxk6KlFkrYwyHgCVdKY+s=
diff --git a/cmd/packserver/main.go b/cmd/packserver/main.go
index c896e42..d71624d 100644
--- a/cmd/packserver/main.go
+++ b/cmd/packserver/main.go
@@ -49,6 +49,8 @@ func main() {
 		"Name of index file (index.html or similar)")
 	rootCmd.Flags().Duration("expiry", 0,
 		"Tell client how long it can cache data for; 0 means no caching")
+	rootCmd.Flags().String("fallback-404", "",
+		"Name of file to return if response would be 404 (spa.html or similar)")
 
 	if err := rootCmd.Execute(); err != nil {
 		fmt.Fprintln(os.Stderr, err)
@@ -124,6 +126,12 @@ func run(c *cobra.Command, args []string) error {
 		return err
 	}
 
+	// optional 404 fallback file
+	fallback404File, err := c.Flags().GetString("fallback-404")
+	if err != nil {
+		return err
+	}
+
 	// verify .htpack specifications
 	if len(args) == 0 {
 		return errors.New("must specify one or more .htpack files")
@@ -157,6 +165,10 @@ func run(c *cobra.Command, args []string) error {
 		if indexFile != "" {
 			packHandler.SetIndex(indexFile)
 		}
+		if err = packHandler.SetNotFound(fallback404File); err != nil {
+			return fmt.Errorf("%s: fallback-404 resource %q "+
+				"not found in packfile", prefix, fallback404File)
+		}
 
 		handler := &addHeaders{
 			extraHeaders: extraHeaders,