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])