diff --git a/Android.mk b/Android.mk
index d529f70..0d9338d 100644
--- a/Android.mk
+++ b/Android.mk
@@ -700,13 +700,10 @@
     $(eval LOCAL_MODULE_PATH := \
         $(TARGET_OUT_DATA_NATIVE_TESTS)/update_engine_unittests/gen) \
     $(eval LOCAL_MODULE_STEM := $(1)) \
-    $(eval my_gen := $(call local-intermediates-dir)/gen/$(1)) \
-    $(eval $(my_gen) : PRIVATE_CUSTOM_TOOL = \
-        tar -jxf $$< -C $$(dir $$@) $$(notdir $$@) && touch $$@) \
-    $(eval $(my_gen) : $(LOCAL_PATH)/sample_images/sample_images.tar.bz2 ; \
-        $$(transform-generated-source)) \
-    $(eval LOCAL_PREBUILT_MODULE_FILE := $(my_gen)) \
-    $(eval include $(BUILD_PREBUILT))
+    $(eval include $(BUILD_SYSTEM)/base_rules.mk) \
+    $(eval $(LOCAL_BUILT_MODULE) : \
+        $(LOCAL_PATH)/sample_images/sample_images.tar.bz2 ; \
+        tar -jxf $$< -C $$(dir $$@) $$(notdir $$@) && touch $$@)
 endef
 
 $(call ue-unittest-sample-image,disk_ext2_1k.img)
diff --git a/sample_images/generate_images.sh b/sample_images/generate_images.sh
index 1c2a83c..17bb11c 100755
--- a/sample_images/generate_images.sh
+++ b/sample_images/generate_images.sh
@@ -184,7 +184,7 @@
   # Generate the tarball and delete temporary images.
   echo "Packing tar file sample_images.tar.bz2"
   tar -jcf "${OUTPUT_DIR}/sample_images.tar.bz2" -C "${OUTPUT_DIR}" \
-    "${IMAGES[@]}"
+    --sparse "${IMAGES[@]}"
   cd "${OUTPUT_DIR}"
   rm "${IMAGES[@]}"
 }
diff --git a/sample_images/sample_images.tar.bz2 b/sample_images/sample_images.tar.bz2
index 83141ab..fe1a80a 100644
--- a/sample_images/sample_images.tar.bz2
+++ b/sample_images/sample_images.tar.bz2
Binary files differ