diff --git a/disklock.lua b/disklock.lua
index 231418c..82b9346 100644
--- a/disklock.lua
+++ b/disklock.lua
@@ -28,13 +28,14 @@ local function deepcopy(o, seen)
 end
 
 local realfs = deepcopy(fs)
-local function getRom(path)
-    if not path then path = "/rom" end
+local rom_cache = nil
+
+local function buildRom(path)
     local out = {}
-    for _,file in ipairs(realfs.list(path)) do
-        local fullPath = realfs.combine(path, file) -- use realfs here to avoid recursing into _G.fs
+    for _, file in ipairs(realfs.list(path)) do
+        local fullPath = realfs.combine(path, file)
         if realfs.isDir(fullPath) then
-            out[file] = getRom(fullPath)
+            out[file] = buildRom(fullPath)
         else
             local handle = realfs.open(fullPath, "r")
             out[file] = handle.readAll()
@@ -44,6 +45,13 @@ local function getRom(path)
     return out
 end
 
+local function getRom()
+    if not rom_cache then
+        rom_cache = buildRom("/rom")
+    end
+    return rom_cache
+end
+
 local function getFileSystem()
     if filesystem then filesystem.rom = getRom() return filesystem end
     if not realfs.exists("fs") then