diff --git a/.github/cloudbuild/flutter-android.yaml b/.github/cloudbuild/flutter-android.yaml
index a6397ae5e..3bdbed244 100644
--- a/.github/cloudbuild/flutter-android.yaml
+++ b/.github/cloudbuild/flutter-android.yaml
@@ -1,5 +1,9 @@
 substitutions:
   _IMAGE_NAME: mlperf-mobile-flutter-android
+# Building apks with flutter requires a lot of memory.
+# Builds on standard machines with 4GB of RAM can unexpectedly hang.
+# Also the build is mostly CPU-intensive, so using 8-core machines
+# reduces build time up to 3 times.
 options:
  machineType: 'E2_HIGHCPU_8'
 
diff --git a/flutter/Makefile b/flutter/Makefile
index cdba44710..231ad1835 100644
--- a/flutter/Makefile
+++ b/flutter/Makefile
@@ -49,11 +49,14 @@ android: backend-bridge-android backends/tflite-android prepare-flutter
 .PHONY: android/apk
 android/apk: android
 	flutter clean
+	@# take results from build/app/outputs/flutter-apk/app-release.apk
 	flutter build apk
 
 .PHONY: ci/android/test_apk
 ci/android/test_apk: android/apk
+	@# take results from build/app/outputs/apk/androidTest/debug/app-debug-androidTest.apk
 	cd android && ./gradlew app:assembleAndroidTest
+	@# take results from build/app/outputs/apk/debug/app-debug.apk
 	cd android && ./gradlew app:assembleDebug -Ptarget=integration_test/first_test.dart
 
 .PHONY: docker/android/apk