diff --git a/sumdb/cmd/proxy.go b/sumdb/cmd/proxy.go
index e58c71a..ebaa80b 100644
--- a/sumdb/cmd/proxy.go
+++ b/sumdb/cmd/proxy.go
@@ -26,19 +26,18 @@ import (
 )
 
 var (
-	listen = flag.String("listen", ":8089", "Address to set up HTTP server listening on")
-)
-
-const (
-	upstreamBase = "https://sum.golang.org"
+	listen      = flag.String("listen", ":8089", "Address to set up HTTP server listening on")
+	witnessSigs = flag.Uint("witnesses", 0, "Number of witness signatures required on a checkpoint. Setting this will pull checkpoints from the transparency-dev prod distributor.")
 )
 
 func main() {
 	klog.InitFlags(nil)
 	flag.Parse()
 
-	proxy := sumdb.NewProxy(sumdb.ProxyOpts{})
-	klog.Infof("Proxying tlog-tiles API to %s on %s", upstreamBase, *listen)
+	proxy := sumdb.NewProxy(sumdb.ProxyOpts{
+		WitnessSigs: *witnessSigs,
+	})
+	klog.Infof("tlog-tiles API listening on %s", *listen)
 	if err := http.ListenAndServe(*listen, proxy); err != nil {
 		klog.Fatalf("ListenAndServe: %v", err)
 	}
diff --git a/sumdb/proxy.go b/sumdb/proxy.go
index b1fe943..6d6f611 100644
--- a/sumdb/proxy.go
+++ b/sumdb/proxy.go
@@ -31,13 +31,23 @@ import (
 )
 
 const (
-	upstreamBase = "https://sum.golang.org"
+	upstreamBase                 = "https://sum.golang.org"
+	distributorBase              = "https://api.transparency.dev/"
+	distributorCheckpointPathFmt = "/distributor/v0/logs/a32d071739c062f4973f1db8cc1069f517428d77105962b285bbf918c4062591/checkpoint.%d"
 )
 
 type ProxyOpts struct {
 	// PathPrefix should be set if the proxy is hosted not at "/".
 	// Any path beyond this should be set here, so that it can be stripped.
 	PathPrefix string
+
+	// WitnessSigs should be set to ensure that a given number of witness signatures
+	// are available. If this is left at the default of 0, then we proxy to the
+	// latest checkpoint from SumDB. If this is set to a positive number, then we
+	// request the latest checkpoint with that number of sigs from the checkpoint
+	// distributor.
+	// https://github.com/transparency-dev/distributor/
+	WitnessSigs uint
 }
 
 func NewProxy(opts ProxyOpts) *httputil.ReverseProxy {
@@ -45,6 +55,10 @@ func NewProxy(opts ProxyOpts) *httputil.ReverseProxy {
 	if err != nil {
 		klog.Fatalf("Failed to parse upstream URL %q: %v", upstreamBase, err)
 	}
+	distributor, err := url.Parse(distributorBase)
+	if err != nil {
+		klog.Fatalf("Failed to parse distributor URL %q: %v", distributorBase, err)
+	}
 
 	prefix, _ := strings.CutSuffix(opts.PathPrefix, "/")
 
@@ -60,7 +74,12 @@ func NewProxy(opts ProxyOpts) *httputil.ReverseProxy {
 			klog.V(2).Infof("Request for %s", inPath)
 
 			if inPath == "/checkpoint" {
-				r.Out.URL.Path = "/latest"
+				if opts.WitnessSigs == 0 {
+					r.Out.URL.Path = "/latest"
+					return
+				}
+				r.SetURL(distributor)
+				r.Out.URL.Path = fmt.Sprintf(distributorCheckpointPathFmt, opts.WitnessSigs)
 			} else if strings.HasPrefix(inPath, tlogEntriesPrefix) {
 				o := strings.TrimPrefix(inPath, tlogEntriesPrefix)
 				r.Out.URL.Path = fmt.Sprintf("%s%s", sumDBTileDataPrefix, o)
diff --git a/vindex/cmd/sumdb/main.go b/vindex/cmd/sumdb/main.go
index 6a58b0b..6ff4c4f 100644
--- a/vindex/cmd/sumdb/main.go
+++ b/vindex/cmd/sumdb/main.go
@@ -47,6 +47,7 @@ var (
 	outputLogPrivKeyFile = flag.String("output_log_private_key_path", "", "Location of private key file. If unset, uses the contents of the OUTPUT_LOG_PRIVATE_KEY environment variable.")
 	storageDir           = flag.String("storage_dir", "", "Root directory in which to store the data for the demo. This will create subdirectories for the Output Log, and allocate space to store the verifiable map persistence.")
 	persistIndex         = flag.Bool("persist_index", false, "Set to true to use a disk-based implementation of the verifiable index. This can be slow, but useful in situations where memory is constrained.")
+	witnessSigs          = flag.Uint("witnesses", 0, "Number of witness signatures required on the SumDB checkpoint. Setting this will pull checkpoints from the transparency-dev prod distributor.")
 	listen               = flag.String("listen", ":8088", "Address to set up HTTP server listening on")
 )
 
@@ -106,7 +107,8 @@ func run(ctx context.Context) error {
 		return err
 	}
 	sumProxy := sumdb.NewProxy(sumdb.ProxyOpts{
-		PathPrefix: "/inputlog/",
+		PathPrefix:  "/inputlog/",
+		WitnessSigs: *witnessSigs,
 	})
 
 	outputLog, outputCloser := outputLogOrDie(ctx, outputLogDir)