diff --git a/updater_sample/Android.mk b/updater_sample/Android.mk
index 7662111..463dbb3 100644
--- a/updater_sample/Android.mk
+++ b/updater_sample/Android.mk
@@ -21,8 +21,7 @@
 LOCAL_MODULE_TAGS := samples
 LOCAL_SDK_VERSION := system_current
 
-# TODO: enable proguard and use proguard.flags file
-LOCAL_PROGUARD_ENABLED := disabled
+LOCAL_PROGUARD_FLAG_FILES := proguard.flags
 
 LOCAL_SRC_FILES := $(call all-java-files-under, src)
 
diff --git a/updater_sample/proguard.flags b/updater_sample/proguard.flags
new file mode 100644
index 0000000..97ab534
--- /dev/null
+++ b/updater_sample/proguard.flags
@@ -0,0 +1,24 @@
+# Copyright (C) 2018 The Android Open Source Project
+#
+# 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.
+
+# Keep, used in tests.
+-keep public class com.example.android.systemupdatersample.UpdateManager {
+   public int getUpdaterState();
+}
+
+# Keep, used in tests.
+-keep public class com.example.android.systemupdatersample.UpdateConfig {
+   public <init>(java.lang.String, java.lang.String, int);
+}
+
diff --git a/updater_sample/tests/Android.mk b/updater_sample/tests/Android.mk
index 9aec372..4157604 100644
--- a/updater_sample/tests/Android.mk
+++ b/updater_sample/tests/Android.mk
@@ -22,10 +22,10 @@
 LOCAL_MODULE_TAGS := tests
 LOCAL_JAVA_LIBRARIES := \
     android.test.base.stubs \
-    android.test.runner.stubs \
-    guava
+    android.test.runner.stubs
 LOCAL_STATIC_JAVA_LIBRARIES := android-support-test \
-    mockito-target-minus-junit4
+    mockito-target-minus-junit4 \
+    guava
 LOCAL_INSTRUMENTATION_FOR := SystemUpdaterSample
 LOCAL_PROGUARD_ENABLED := disabled