diff --git a/moon/init.lua b/moon/init.lua
index 4e0d68f..b6178db 100644
--- a/moon/init.lua
+++ b/moon/init.lua
@@ -2,7 +2,33 @@ if not moon or not moon.inject then
   module("moon", package.seeall)
 end
 local util = require("moonscript.util")
+local lua = {
+  debug = debug
+}
 dump = util.dump
+debug = {
+  upvalue = function(fn, k, v)
+    local upvalues = { }
+    local i = 1
+    while true do
+      local name = lua.debug.getupvalue(fn, i)
+      if name == nil then
+        break
+      end
+      upvalues[name] = i
+      i = i + 1
+    end
+    if not upvalues[k] then
+      error("Failed to find upvalue: " .. tostring(k))
+    end
+    if not v then
+      local _, value = lua.debug.getupvalue(fn, upvalues[k])
+      return value
+    else
+      return lua.debug.setupvalue(fn, upvalues[k], v)
+    end
+  end
+}
 run_with_scope = function(fn, scope, ...)
   local old_env = getfenv(fn)
   local env = setmetatable({ }, {
diff --git a/moon/init.moon b/moon/init.moon
index adf0eed..84f496b 100644
--- a/moon/init.moon
+++ b/moon/init.moon
@@ -4,10 +4,33 @@ if not moon or not moon.inject
 
 util = require "moonscript.util"
 
+lua = { :debug }
+
 export *
 
 dump = util.dump
 
+debug = {
+  upvalue: (fn, k, v) ->
+    upvalues = {}
+    i = 1
+    while true
+      name = lua.debug.getupvalue(fn, i)
+      break if name == nil
+      upvalues[name] = i
+      i += 1
+
+    if not upvalues[k]
+      error "Failed to find upvalue: " .. tostring k
+
+    if not v
+      _, value = lua.debug.getupvalue fn, upvalues[k]
+      value
+    else
+      lua.debug.setupvalue fn, upvalues[k], v
+}
+
+
 -- run a function with scope injected before its function environment
 run_with_scope = (fn, scope, ...) ->
   old_env = getfenv fn