diff --git a/src/mods/Sandbox.lua b/src/mods/Sandbox.lua
index e41190ba..f52a07ce 100644
--- a/src/mods/Sandbox.lua
+++ b/src/mods/Sandbox.lua
@@ -28,8 +28,14 @@ local DENIED = {
 }
 
 -- Same idea one level up: love.filesystem is reachable by name, and
--- love.thread starts a Lua state this sandbox has no say over.
-local DENIED_PREFIX = { ["love"] = true, ["ffi"] = true }
+-- love.thread starts a Lua state this sandbox has no say over.  jit.util
+-- is the LuaJIT-specific equal of the debug library above -- funcbc,
+-- funck and friends read the bytecode and constants of any function a
+-- chunk can reach, which is enough to walk back to upvalues (the real
+-- _G, love, io) the rest of this file exists to keep out of reach.  The
+-- bare `jit` table stays -- env.jit above hands it over directly for
+-- jit.on/off/flush -- so only the submodule require is denied.
+local DENIED_PREFIX = { ["love"] = true, ["ffi"] = true, ["jit"] = true }
 
 -- The wire, which is what the network permission governs.
 local NETWORK = { socket = true, enet = true, http = true, https = true,
diff --git a/tests/modkit/cases/sandbox.lua b/tests/modkit/cases/sandbox.lua
index 27133e15..5f9c06c8 100644
--- a/tests/modkit/cases/sandbox.lua
+++ b/tests/modkit/cases/sandbox.lua
@@ -44,6 +44,11 @@ local PROBE = [[
   out.requireDebug = attempt(require, "debug")
   out.requirePackage = attempt(require, "package")
   out.requireFfi = attempt(require, "ffi")
+  -- jit.util exposes bytecode/constant introspection over any function this
+  -- chunk can reach -- the same class of escape the debug library is denied
+  -- for -- so it must fail the same way require("debug") does rather than
+  -- walking straight through under the bare "jit" global's cover.
+  out.requireJitUtil = attempt(require, "jit.util")
   out.requireSocket = attempt(require, "socket")
   out.requireSemver = select(2, pcall(require, "src.mods.Semver"))
 
@@ -180,6 +185,8 @@ T.eq(out.getfenv, nil, "getfenv is still absent, so a mod cannot read the real _
 T.eq(out.debug, nil, "the debug library is still absent")
 T.check(out.loveThread ~= false, "love.thread is still refused: it opens a full Lua state")
 T.check(out.requireFfi ~= false, "require(\"ffi\") is still refused: it is arbitrary C")
+T.check(out.requireJitUtil ~= false,
+  "require(\"jit.util\") is still refused: it is bytecode/constant introspection")
 T.check(out.requireDebug ~= false, "require(\"debug\") is still refused")
 T.check(out.requirePackage ~= false, "require(\"package\") is still refused")
 T.eq(out.popen, nil, "io.popen refuses rather than spawning a process")