diff --git a/cmd/multiproduct_kati/main.go b/cmd/multiproduct_kati/main.go
index 9cb75fa..6a3d579 100644
--- a/cmd/multiproduct_kati/main.go
+++ b/cmd/multiproduct_kati/main.go
@@ -393,6 +393,9 @@
 
 	config := build.NewConfig(ctx, flag.Args()...)
 	config.Environment().Set("OUT_DIR", outDir)
+	if !*keepArtifacts {
+		config.Environment().Set("EMPTY_NINJA_FILE", "true")
+	}
 	build.FindSources(ctx, config, mpctx.Finder)
 	config.Lunch(ctx, product, *buildVariant)
 
@@ -413,12 +416,7 @@
 				log.Fatalf("Error zipping artifacts: %v", err)
 			}
 		}
-		if *incremental {
-			// Save space, Kati doesn't notice
-			if f := config.KatiBuildNinjaFile(); f != "" {
-				os.Truncate(f, 0)
-			}
-		} else {
+		if !*incremental {
 			os.RemoveAll(outDir)
 		}
 	}()
diff --git a/ui/build/config.go b/ui/build/config.go
index 840f505..5a6d5db 100644
--- a/ui/build/config.go
+++ b/ui/build/config.go
@@ -143,6 +143,9 @@
 		"ANDROID_DEV_SCRIPTS",
 		"ANDROID_EMULATOR_PREBUILTS",
 		"ANDROID_PRE_BUILD_PATHS",
+
+		// Only set in multiproduct_kati after config generation
+		"EMPTY_NINJA_FILE",
 	)
 
 	// Tell python not to spam the source tree with .pyc files.
diff --git a/ui/build/kati.go b/ui/build/kati.go
index 56e9a88..d2e9fe9 100644
--- a/ui/build/kati.go
+++ b/ui/build/kati.go
@@ -81,6 +81,10 @@
 		"--kati_stats",
 	}, args...)
 
+	if config.Environment().IsEnvTrue("EMPTY_NINJA_FILE") {
+		args = append(args, "--empty_ninja_file")
+	}
+
 	cmd := Command(ctx, config, "ckati", executable, args...)
 	cmd.Sandbox = katiSandbox
 	pipe, err := cmd.StdoutPipe()