diff --git a/ui/build/build.go b/ui/build/build.go
index 422b95f60..14d23a7da 100644
--- a/ui/build/build.go
+++ b/ui/build/build.go
@@ -15,13 +15,11 @@
 package build
 
 import (
-	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
 	"sync"
 	"text/template"
-	"time"
 
 	"android/soong/ui/metrics"
 )
@@ -58,31 +56,6 @@ func SetupOutDir(ctx Context, config Config) {
 	} else {
 		ctx.Fatalln("Missing BUILD_DATETIME_FILE")
 	}
-
-	// BUILD_NUMBER should be set to the source control value that
-	// represents the current state of the source code.  E.g., a
-	// perforce changelist number or a git hash.  Can be an arbitrary string
-	// (to allow for source control that uses something other than numbers),
-	// but must be a single word and a valid file name.
-	//
-	// If no BUILD_NUMBER is set, create a useful "I am an engineering build
-	// from this date/time" value.  Make it start with a non-digit so that
-	// anyone trying to parse it as an integer will probably get "0".
-	buildNumber, ok := config.environ.Get("BUILD_NUMBER")
-	if ok {
-		writeValueIfChanged(ctx, config, config.OutDir(), "file_name_tag.txt", buildNumber)
-	} else {
-		var username string
-		if username, ok = config.environ.Get("BUILD_USERNAME"); !ok {
-			ctx.Fatalln("Missing BUILD_USERNAME")
-		}
-		buildNumber = fmt.Sprintf("eng.%.6s.%s", username, time.Now().Format("20060102.150405" /* YYYYMMDD.HHMMSS */))
-		writeValueIfChanged(ctx, config, config.OutDir(), "file_name_tag.txt", username)
-	}
-	// Write the build number to a file so it can be read back in
-	// without changing the command line every time.  Avoids rebuilds
-	// when using ninja.
-	writeValueIfChanged(ctx, config, config.SoongOutDir(), "build_number.txt", buildNumber)
 }
 
 var combinedBuildNinjaTemplate = template.Must(template.New("combined").Parse(`
diff --git a/ui/build/config.go b/ui/build/config.go
index f80868c33..084d28d83 100644
--- a/ui/build/config.go
+++ b/ui/build/config.go
@@ -22,7 +22,6 @@ import (
 	"math/rand"
 	"os"
 	"os/exec"
-	"os/user"
 	"path/filepath"
 	"runtime"
 	"strconv"
@@ -456,16 +455,6 @@ func NewConfig(ctx Context, args ...string) Config {
 
 	ret.environ.Set("BUILD_DATETIME_FILE", buildDateTimeFile)
 
-	if _, ok := ret.environ.Get("BUILD_USERNAME"); !ok {
-		username := "unknown"
-		if u, err := user.Current(); err == nil {
-			username = u.Username
-		} else {
-			ctx.Println("Failed to get current user:", err)
-		}
-		ret.environ.Set("BUILD_USERNAME", username)
-	}
-
 	if ret.UseRBE() {
 		for k, v := range getRBEVars(ctx, Config{ret}) {
 			ret.environ.Set(k, v)
diff --git a/ui/build/kati.go b/ui/build/kati.go
index 31e744029..aea56d31a 100644
--- a/ui/build/kati.go
+++ b/ui/build/kati.go
@@ -15,8 +15,6 @@
 package build
 
 import (
-	"android/soong/ui/metrics"
-	"android/soong/ui/status"
 	"crypto/md5"
 	"fmt"
 	"io/ioutil"
@@ -24,6 +22,10 @@ import (
 	"os/user"
 	"path/filepath"
 	"strings"
+	"time"
+
+	"android/soong/ui/metrics"
+	"android/soong/ui/status"
 )
 
 var spaceSlashReplacer = strings.NewReplacer("/", "_", " ", "_")
@@ -196,14 +198,32 @@ func runKati(ctx Context, config Config, extraSuffix string, args []string, envF
 		}
 	}
 	writeValueIfChanged(ctx, config, config.SoongOutDir(), "build_hostname.txt", hostname)
-	_, ok = cmd.Environment.Get("BUILD_NUMBER")
+
+	// BUILD_NUMBER should be set to the source control value that
+	// represents the current state of the source code.  E.g., a
+	// perforce changelist number or a git hash.  Can be an arbitrary string
+	// (to allow for source control that uses something other than numbers),
+	// but must be a single word and a valid file name.
+	//
+	// If no BUILD_NUMBER is set, create a useful "I am an engineering build
+	// from this date/time" value.  Make it start with a non-digit so that
+	// anyone trying to parse it as an integer will probably get "0".
+	cmd.Environment.Unset("HAS_BUILD_NUMBER")
+	buildNumber, ok := cmd.Environment.Get("BUILD_NUMBER")
 	// Unset BUILD_NUMBER during kati run to avoid kati rerun, kati will use BUILD_NUMBER from a file.
 	cmd.Environment.Unset("BUILD_NUMBER")
 	if ok {
 		cmd.Environment.Set("HAS_BUILD_NUMBER", "true")
+		writeValueIfChanged(ctx, config, config.OutDir(), "file_name_tag.txt", buildNumber)
 	} else {
+		buildNumber = fmt.Sprintf("eng.%.6s.%s", username, time.Now().Format("20060102.150405" /* YYYYMMDD.HHMMSS */))
 		cmd.Environment.Set("HAS_BUILD_NUMBER", "false")
+		writeValueIfChanged(ctx, config, config.OutDir(), "file_name_tag.txt", username)
 	}
+	// Write the build number to a file so it can be read back in
+	// without changing the command line every time.  Avoids rebuilds
+	// when using ninja.
+	writeValueIfChanged(ctx, config, config.SoongOutDir(), "build_number.txt", buildNumber)
 
 	// Apply the caller's function closure to mutate the environment variables.
 	envFunc(cmd.Environment)