diff --git a/sandbox.lua b/sandbox.lua
index 72ce806..98fde7f 100644
--- a/sandbox.lua
+++ b/sandbox.lua
@@ -54,7 +54,11 @@ local function cleanup()
 end
 
 local function run(f, options)
-  if type(f) == 'string' then f = loadstring(f) end
+  if type(f) == 'string' then f = assert(loadstring(f)) end
+
+  options = options or {}
+
+  local limit = options.limit or 500000
 
   setfenv(f, BASE_ENV)
 
@@ -65,8 +69,8 @@ local function run(f, options)
   local step = 1
   local count = 0
   local timeout = function(str)
-    count = count + step
-    if count >= 500000 then
+    count = count + 1
+    if count >= limit then
       cleanup()
       error('Timeout')
     end
@@ -87,4 +91,4 @@ end
 local sandbox = { run = run }
 
 
-return setmetatable(sandbox, {__call = function(_,f) return run(f) end})
+return setmetatable(sandbox, {__call = function(_,f,o) return run(f,o) end})
diff --git a/spec/sandbox_spec.lua b/spec/sandbox_spec.lua
index c5c4963..911246b 100644
--- a/spec/sandbox_spec.lua
+++ b/spec/sandbox_spec.lua
@@ -38,10 +38,16 @@ describe('sandbox', function()
     assert.equal('hellohello', string.rep('hello', 2))
   end)
 
-  it('#focus throws an error with infinite loops', function()
-    assert.has_error(function() sandbox("while true do end") end)
+
+  describe('when handling infinite loops', function()
+    it('throws an error with infinite loops', function()
+      assert.has_error(function() sandbox("while true do end") end)
+    end)
+
+    it('#focus accepts a limit param', function()
+      --assert.no_has_error(function() sandbox("for i=1,10000 do end") end)
+      assert.has_error(function() sandbox("for i=1,10000 do end", {limit = 50}) end)
+    end)
   end)
 
-
-
 end)