diff --git a/misc/dashboard/app/build/build.go b/misc/dashboard/app/build/build.go
index 8dbefe9d38..7b73a25215 100644
--- a/misc/dashboard/app/build/build.go
+++ b/misc/dashboard/app/build/build.go
@@ -262,6 +262,13 @@ func (t *Tag) Valid() os.Error {
 	return nil
 }
 
+// Commit returns the Commit that corresponds with this Tag.
+func (t *Tag) Commit(c appengine.Context) (*Commit, os.Error) {
+	com := &Commit{Hash: t.Hash}
+	err := datastore.Get(c, com.Key(c), com)
+	return com, err
+}
+
 // GetTag fetches a Tag by name from the datastore.
 func GetTag(c appengine.Context, tag string) (*Tag, os.Error) {
 	t := &Tag{Kind: tag}
diff --git a/misc/dashboard/app/build/handler.go b/misc/dashboard/app/build/handler.go
index 9dcf128dc3..4aa161e8d2 100644
--- a/misc/dashboard/app/build/handler.go
+++ b/misc/dashboard/app/build/handler.go
@@ -196,17 +196,44 @@ func buildTodo(c appengine.Context, builder, packagePath, goHash string) (interf
 		Run(c)
 	for {
 		com := new(Commit)
-		if _, err := t.Next(com); err != nil {
-			if err == datastore.Done {
-				err = nil
-			}
+		if _, err := t.Next(com); err == datastore.Done {
+			break
+		} else if err != nil {
 			return nil, err
 		}
 		if com.Result(builder, goHash) == nil {
 			return com, nil
 		}
 	}
-	panic("unreachable")
+
+	// Nothing left to do if this is a package (not the Go tree).
+	if packagePath != "" {
+		return nil, nil
+	}
+
+	// If there are no Go tree commits left to build,
+	// see if there are any subrepo commits that need to be built at tip.
+	// If so, ask the builder to build a go tree at the tip commit.
+	// TODO(adg): do the same for "weekly" and "release" tags.
+	tag, err := GetTag(c, "tip")
+	if err != nil {
+		return nil, err
+	}
+	pkgs, err := Packages(c, "subrepo")
+	if err != nil {
+		return nil, err
+	}
+	for _, pkg := range pkgs {
+		com, err := pkg.LastCommit(c)
+		if err != nil {
+			c.Warningf("%v: no Commit found: %v", pkg, err)
+			continue
+		}
+		if com.Result(builder, tag.Hash) == nil {
+			return tag.Commit(c)
+		}
+	}
+	return nil, nil
 }
 
 // packagesHandler returns a list of the non-Go Packages monitored
diff --git a/misc/dashboard/app/build/test.go b/misc/dashboard/app/build/test.go
index f22eac1a49..6f17de02bc 100644
--- a/misc/dashboard/app/build/test.go
+++ b/misc/dashboard/app/build/test.go
@@ -109,7 +109,11 @@ var testRequests = []struct {
 	{"/result", nil, &Result{PackagePath: testPkg, Builder: "linux-386", Hash: "1001", GoHash: "0001", OK: true}, nil},
 	{"/todo", url.Values{"kind": {"build-package"}, "builder": {"linux-386"}, "packagePath": {testPkg}, "goHash": {"0001"}}, nil, nil},
 	{"/todo", url.Values{"kind": {"build-package"}, "builder": {"linux-386"}, "packagePath": {testPkg}, "goHash": {"0002"}}, nil, &Todo{Kind: "build-package", Data: &Commit{Hash: "1003"}}},
+
+	// re-build Go revision for stale subrepos
+	{"/todo", url.Values{"kind": {"build-go-commit"}, "builder": {"linux-386"}}, nil, &Todo{Kind: "build-go-commit", Data: &Commit{Hash: "0005"}}},
 	{"/result", nil, &Result{PackagePath: testPkg, Builder: "linux-386", Hash: "1001", GoHash: "0005", OK: false, Log: "boo"}, nil},
+	{"/todo", url.Values{"kind": {"build-go-commit"}, "builder": {"linux-386"}}, nil, nil},
 }
 
 func testHandler(w http.ResponseWriter, r *http.Request) {
@@ -215,8 +219,8 @@ func testHandler(w http.ResponseWriter, r *http.Request) {
 				errorf("Response.Data not *Commit: %T", g.Data)
 				return
 			}
-			if e.Data.(*Commit).Hash != gd.Hash {
-				errorf("hashes don't match: got %q, want %q", g, e)
+			if eh := e.Data.(*Commit).Hash; eh != gd.Hash {
+				errorf("hashes don't match: got %q, want %q", gd.Hash, eh)
 				return
 			}
 		}
diff --git a/misc/dashboard/app/build/ui.go b/misc/dashboard/app/build/ui.go
index 37a1500633..bc5a703455 100644
--- a/misc/dashboard/app/build/ui.go
+++ b/misc/dashboard/app/build/ui.go
@@ -145,7 +145,7 @@ func TagState(c appengine.Context, name string) ([]*PackageState, os.Error) {
 	for _, pkg := range pkgs {
 		commit, err := pkg.LastCommit(c)
 		if err != nil {
-			c.Errorf("no Commit found: %v", pkg)
+			c.Warningf("%v: no Commit found: %v", pkg, err)
 			continue
 		}
 		results := commit.Results(tag.Hash)