diff --git a/tests/common/test_constants.h b/tests/common/test_constants.h
index 93e4ab5..f6b6922 100644
--- a/tests/common/test_constants.h
+++ b/tests/common/test_constants.h
@@ -22,6 +22,8 @@
 // Zip entries in ziptest_valid.zip.
 static const std::string kATxtContents("abcdefghabcdefgh\n");
 static const std::string kBTxtContents("abcdefgh\n");
+static const std::string kCTxtContents("abcdefghabcdefgh\n");
+static const std::string kDTxtContents("abcdefgh\n");
 
 // echo -n -e "abcdefghabcdefgh\n" | sha1sum
 static const std::string kATxtSha1Sum("32c96a03dc8cd20097940f351bca6261ee5a1643");
diff --git a/tests/component/updater_test.cpp b/tests/component/updater_test.cpp
index d34c0e5..cd28572 100644
--- a/tests/component/updater_test.cpp
+++ b/tests/component/updater_test.cpp
@@ -270,6 +270,102 @@
     ASSERT_EQ(0, unlink(src2.c_str()));
 }
 
+TEST_F(UpdaterTest, package_extract_dir) {
+  // package_extract_dir expects 2 arguments.
+  expect(nullptr, "package_extract_dir()", kArgsParsingFailure);
+  expect(nullptr, "package_extract_dir(\"arg1\")", kArgsParsingFailure);
+  expect(nullptr, "package_extract_dir(\"arg1\", \"arg2\", \"arg3\")", kArgsParsingFailure);
+
+  std::string zip_path = from_testdata_base("ziptest_valid.zip");
+  ZipArchiveHandle handle;
+  ASSERT_EQ(0, OpenArchive(zip_path.c_str(), &handle));
+
+  // Need to set up the ziphandle.
+  UpdaterInfo updater_info;
+  updater_info.package_zip = handle;
+
+  // Extract "b/c.txt" and "b/d.txt" with package_extract_dir("b", "<dir>").
+  TemporaryDir td;
+  std::string temp_dir(td.path);
+  std::string script("package_extract_dir(\"b\", \"" + temp_dir + "\")");
+  expect("t", script.c_str(), kNoCause, &updater_info);
+
+  // Verify.
+  std::string data;
+  std::string file_c = temp_dir + "/c.txt";
+  ASSERT_TRUE(android::base::ReadFileToString(file_c, &data));
+  ASSERT_EQ(kCTxtContents, data);
+
+  std::string file_d = temp_dir + "/d.txt";
+  ASSERT_TRUE(android::base::ReadFileToString(file_d, &data));
+  ASSERT_EQ(kDTxtContents, data);
+
+  // Modify the contents in order to retry. It's expected to be overwritten.
+  ASSERT_TRUE(android::base::WriteStringToFile("random", file_c));
+  ASSERT_TRUE(android::base::WriteStringToFile("random", file_d));
+
+  // Extract again and verify.
+  expect("t", script.c_str(), kNoCause, &updater_info);
+
+  ASSERT_TRUE(android::base::ReadFileToString(file_c, &data));
+  ASSERT_EQ(kCTxtContents, data);
+  ASSERT_TRUE(android::base::ReadFileToString(file_d, &data));
+  ASSERT_EQ(kDTxtContents, data);
+
+  // Clean up the temp files under td.
+  ASSERT_EQ(0, unlink(file_c.c_str()));
+  ASSERT_EQ(0, unlink(file_d.c_str()));
+
+  // Extracting "b/" (with slash) should give the same result.
+  script = "package_extract_dir(\"b/\", \"" + temp_dir + "\")";
+  expect("t", script.c_str(), kNoCause, &updater_info);
+
+  ASSERT_TRUE(android::base::ReadFileToString(file_c, &data));
+  ASSERT_EQ(kCTxtContents, data);
+  ASSERT_TRUE(android::base::ReadFileToString(file_d, &data));
+  ASSERT_EQ(kDTxtContents, data);
+
+  ASSERT_EQ(0, unlink(file_c.c_str()));
+  ASSERT_EQ(0, unlink(file_d.c_str()));
+
+  // Extracting "" is allowed. The entries will carry the path name.
+  script = "package_extract_dir(\"\", \"" + temp_dir + "\")";
+  expect("t", script.c_str(), kNoCause, &updater_info);
+
+  std::string file_a = temp_dir + "/a.txt";
+  ASSERT_TRUE(android::base::ReadFileToString(file_a, &data));
+  ASSERT_EQ(kATxtContents, data);
+  std::string file_b = temp_dir + "/b.txt";
+  ASSERT_TRUE(android::base::ReadFileToString(file_b, &data));
+  ASSERT_EQ(kBTxtContents, data);
+  std::string file_b_c = temp_dir + "/b/c.txt";
+  ASSERT_TRUE(android::base::ReadFileToString(file_b_c, &data));
+  ASSERT_EQ(kCTxtContents, data);
+  std::string file_b_d = temp_dir + "/b/d.txt";
+  ASSERT_TRUE(android::base::ReadFileToString(file_b_d, &data));
+  ASSERT_EQ(kDTxtContents, data);
+
+  ASSERT_EQ(0, unlink(file_a.c_str()));
+  ASSERT_EQ(0, unlink(file_b.c_str()));
+  ASSERT_EQ(0, unlink(file_b_c.c_str()));
+  ASSERT_EQ(0, unlink(file_b_d.c_str()));
+  ASSERT_EQ(0, rmdir((temp_dir + "/b").c_str()));
+
+  // Extracting non-existent entry should still give "t".
+  script = "package_extract_dir(\"doesntexist\", \"" + temp_dir + "\")";
+  expect("t", script.c_str(), kNoCause, &updater_info);
+
+  // Only relative zip_path is allowed.
+  script = "package_extract_dir(\"/b\", \"" + temp_dir + "\")";
+  expect("", script.c_str(), kNoCause, &updater_info);
+
+  // Only absolute dest_path is allowed.
+  script = "package_extract_dir(\"b\", \"path\")";
+  expect("", script.c_str(), kNoCause, &updater_info);
+
+  CloseArchive(handle);
+}
+
 // TODO: Test extracting to block device.
 TEST_F(UpdaterTest, package_extract_file) {
   // package_extract_file expects 1 or 2 arguments.
diff --git a/updater/install.cpp b/updater/install.cpp
index da68420..6c11073 100644
--- a/updater/install.cpp
+++ b/updater/install.cpp
@@ -454,28 +454,32 @@
     return StringValue(frac_str);
 }
 
-// package_extract_dir(package_path, destination_path)
-Value* PackageExtractDirFn(const char* name, State* state,
-                          int argc, Expr* argv[]) {
-    if (argc != 2) {
-        return ErrorAbort(state, kArgsParsingFailure, "%s() expects 2 args, got %d", name, argc);
-    }
+// package_extract_dir(package_dir, dest_dir)
+//   Extracts all files from the package underneath package_dir and writes them to the
+//   corresponding tree beneath dest_dir. Any existing files are overwritten.
+//   Example: package_extract_dir("system", "/system")
+//
+//   Note: package_dir needs to be a relative path; dest_dir needs to be an absolute path.
+Value* PackageExtractDirFn(const char* name, State* state, int argc, Expr* argv[]) {
+  if (argc != 2) {
+    return ErrorAbort(state, kArgsParsingFailure, "%s() expects 2 args, got %d", name, argc);
+  }
 
-    std::vector<std::string> args;
-    if (!ReadArgs(state, 2, argv, &args)) {
-        return ErrorAbort(state, kArgsParsingFailure, "%s() Failed to parse the argument(s)", name);
-    }
-    const std::string& zip_path = args[0];
-    const std::string& dest_path = args[1];
+  std::vector<std::string> args;
+  if (!ReadArgs(state, 2, argv, &args)) {
+    return ErrorAbort(state, kArgsParsingFailure, "%s() Failed to parse the argument(s)", name);
+  }
+  const std::string& zip_path = args[0];
+  const std::string& dest_path = args[1];
 
-    ZipArchiveHandle za = ((UpdaterInfo*)(state->cookie))->package_zip;
+  ZipArchiveHandle za = static_cast<UpdaterInfo*>(state->cookie)->package_zip;
 
-    // To create a consistent system image, never use the clock for timestamps.
-    struct utimbuf timestamp = { 1217592000, 1217592000 };  // 8/1/2008 default
+  // To create a consistent system image, never use the clock for timestamps.
+  constexpr struct utimbuf timestamp = { 1217592000, 1217592000 };  // 8/1/2008 default
 
-    bool success = ExtractPackageRecursive(za, zip_path, dest_path, &timestamp, sehandle);
+  bool success = ExtractPackageRecursive(za, zip_path, dest_path, &timestamp, sehandle);
 
-    return StringValue(success ? "t" : "");
+  return StringValue(success ? "t" : "");
 }
 
 // package_extract_file(package_file[, dest_file])