diff --git a/ui/build/ninja.go b/ui/build/ninja.go
new file mode 100644
index 0000000..13e1834
--- /dev/null
+++ b/ui/build/ninja.go
@@ -0,0 +1,78 @@
+// Copyright 2017 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package build
+
+import (
+	"os/exec"
+	"strconv"
+	"strings"
+)
+
+func runNinja(ctx Context, config Config) {
+	executable := "prebuilts/build-tools/" + config.HostPrebuiltTag() + "/bin/ninja"
+	args := []string{
+		"-d", "keepdepfile",
+	}
+
+	args = append(args, config.NinjaArgs()...)
+
+	var parallel int
+	if config.UseGoma() {
+		parallel = config.RemoteParallel()
+	} else {
+		parallel = config.Parallel()
+	}
+	args = append(args, "-j", strconv.Itoa(parallel))
+	if config.keepGoing != 1 {
+		args = append(args, "-k", strconv.Itoa(config.keepGoing))
+	}
+
+	args = append(args, "-f", config.CombinedNinjaFile())
+
+	if config.IsVerbose() {
+		args = append(args, "-v")
+	}
+	args = append(args, "-w", "dupbuild=err")
+
+	env := config.Environment().Copy()
+	env.AppendFromKati(config.KatiEnvFile())
+
+	// Allow both NINJA_ARGS and NINJA_EXTRA_ARGS, since both have been
+	// used in the past to specify extra ninja arguments.
+	if extra, ok := env.Get("NINJA_ARGS"); ok {
+		args = append(args, strings.Fields(extra)...)
+	}
+	if extra, ok := env.Get("NINJA_EXTRA_ARGS"); ok {
+		args = append(args, strings.Fields(extra)...)
+	}
+
+	if _, ok := env.Get("NINJA_STATUS"); !ok {
+		env.Set("NINJA_STATUS", "[%p %f/%t] ")
+	}
+
+	cmd := exec.CommandContext(ctx.Context, executable, args...)
+	cmd.Env = env.Environ()
+	cmd.Stdin = ctx.Stdin()
+	cmd.Stdout = ctx.Stdout()
+	cmd.Stderr = ctx.Stderr()
+	ctx.Verboseln(cmd.Path, cmd.Args)
+	if err := cmd.Run(); err != nil {
+		if e, ok := err.(*exec.ExitError); ok {
+			ctx.Fatalln("ninja failed with:", e.ProcessState.String())
+		} else {
+			ctx.Fatalln("Failed to run ninja:", err)
+		}
+	}
+}