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.