diff --git a/spec/lang/code_gen/fornum_spec.lua b/spec/lang/code_gen/fornum_spec.lua
new file mode 100644
index 00000000..3eaa904f
--- /dev/null
+++ b/spec/lang/code_gen/fornum_spec.lua
@@ -0,0 +1,97 @@
+local util = require("spec.util")
+
+describe("fornum", function()
+   it("5.3: doesn't generate control variable that is local to the iteration", util.gen([[
+      local t: {string} = { "a", "b", "c" }
+
+      for i = 1, #t do
+         i = i + 1
+         print(t[i])
+      end
+   ]], [[
+      local t = { "a", "b", "c" }
+
+      for i = 1, #t do
+         i = i + 1
+         print(t[i])
+      end
+   ]], "5.3"))
+
+   it("5.4: generates control variable that is local to the iteration", util.gen([[
+      local t: {string} = { "a", "b", "c" }
+
+      for i = 1, #t do
+         i = i + 1
+         print(t[i])
+      end
+   ]], [[
+      local t = { "a", "b", "c" }
+
+      for i = 1, #t do local i = i
+         i = i + 1
+         print(t[i])
+      end
+   ]], "5.4"))
+
+   it("5.4: does not generate control variable if not assigned to", util.gen([[
+      local t: {string} = { "a", "b", "c" }
+
+      for i = 1, #t do
+         local j = i + 1
+         print(t[j])
+      end
+   ]], [[
+      local t = { "a", "b", "c" }
+
+      for i = 1, #t do
+         local j = i + 1
+         print(t[j])
+      end
+   ]], "5.4"))
+
+   it("5.4: generates control variable for a loop with a step", util.gen([[
+      for i = 10, 1, -2 do
+         i = i // 2
+         print(i)
+      end
+   ]], [[
+      for i = 10, 1, -2 do local i = i
+         i = i // 2
+         print(i)
+      end
+   ]], "5.4"))
+
+   it("5.4: detects an assignment made from a nested function", util.gen([[
+      for i = 1, 3 do
+         local function bump()
+            i = i + 1
+         end
+         bump()
+         print(i)
+      end
+   ]], [[
+      for i = 1, 3 do local i = i
+         local function bump()
+            i = i + 1
+         end
+         bump()
+         print(i)
+      end
+   ]], "5.4"))
+
+   it("5.4: only shadows the loops that are assigned to", util.gen([[
+      for i = 1, 3 do
+         for j = 1, 3 do
+            j = j + 1
+            print(i, j)
+         end
+      end
+   ]], [[
+      for i = 1, 3 do
+         for j = 1, 3 do local j = j
+            j = j + 1
+            print(i, j)
+         end
+      end
+   ]], "5.4"))
+end)
diff --git a/teal.lua b/teal.lua
index df1fec85..5a0f48a8 100644
--- a/teal.lua
+++ b/teal.lua
@@ -236,6 +236,7 @@ local parse_typeargs_if_any
 
 
 
+
 
 
 local ast = {}
@@ -8486,7 +8487,14 @@ visit_node.cbs = {
          "number"
          self:add_var(node.var, node.var.tk, a_type(node.var, typename, {}))
       end,
-      after = end_scope_and_none_type,
+      after = function(self, node, _children)
+         local var = self:find_var(node.var.tk)
+         if var and var.has_been_written_to then
+            node.fornum_modifies_control_var = true
+         end
+         self:end_scope(node)
+         return NONE
+      end,
    },
    ["return"] = {
       before = function(self, node)
@@ -11154,6 +11162,25 @@ local bit_operators = {
    ["<<"] = "lshift",
 }
 
+
+local function shadow_control_var(node, control_var)
+   if #node.body == 0 then
+      return
+   end
+   local stmt = node_at(node, {
+      kind = "local_declaration",
+      vars = node_at(node, {
+         kind = "variable_list",
+         node_at(node, { kind = "variable", is_lvalue = true, tk = control_var }),
+      }),
+      exps = node_at(node, {
+         kind = "expression_list",
+         node_at(node, { kind = "variable", tk = control_var }),
+      }),
+   })
+   table.insert(node.body, 1, stmt)
+end
+
 local function adjust_code(ast, needs_compat, gen_compat, gen_target)
    local visit = false
 
@@ -11283,24 +11310,15 @@ local function adjust_code(ast, needs_compat, gen_compat, gen_target)
       visit = true
       visit_node.cbs["forin"] = {
          after = function(_, node, _children)
-            if #node.body == 0 then
-               return
-            end
             if node.forin_modifies_control_var then
-               local control_var = node.vars[1].tk
-               local loc_at = node
-               local stmt = node_at(loc_at, {
-                  kind = "local_declaration",
-                  vars = node_at(loc_at, {
-                     kind = "variable_list",
-                     node_at(loc_at, { kind = "variable", is_lvalue = true, tk = control_var }),
-                  }),
-                  exps = node_at(loc_at, {
-                     kind = "expression_list",
-                     node_at(loc_at, { kind = "variable", tk = control_var }),
-                  }),
-               })
-               table.insert(node.body, 1, stmt)
+               shadow_control_var(node, node.vars[1].tk)
+            end
+         end,
+      }
+      visit_node.cbs["fornum"] = {
+         after = function(_, node, _children)
+            if node.fornum_modifies_control_var then
+               shadow_control_var(node, node.var.tk)
             end
          end,
       }
diff --git a/teal/ast.lua b/teal/ast.lua
index ffef498b..feb2a260 100644
--- a/teal/ast.lua
+++ b/teal/ast.lua
@@ -234,6 +234,7 @@ local parse_typeargs_if_any
 
 
 
+
 
 
 local ast = {}
diff --git a/teal/ast.tl b/teal/ast.tl
index 65306fb6..307c857b 100644
--- a/teal/ast.tl
+++ b/teal/ast.tl
@@ -162,6 +162,7 @@ local record Node
    from: Node
    to: Node
    step: Node
+   fornum_modifies_control_var: boolean
 
    -- forin
    vars: Node
diff --git a/teal/check/visitors.lua b/teal/check/visitors.lua
index 9c1399ee..2db4c422 100644
--- a/teal/check/visitors.lua
+++ b/teal/check/visitors.lua
@@ -1217,7 +1217,14 @@ visit_node.cbs = {
          "number"
          self:add_var(node.var, node.var.tk, a_type(node.var, typename, {}))
       end,
-      after = end_scope_and_none_type,
+      after = function(self, node, _children)
+         local var = self:find_var(node.var.tk)
+         if var and var.has_been_written_to then
+            node.fornum_modifies_control_var = true
+         end
+         self:end_scope(node)
+         return NONE
+      end,
    },
    ["return"] = {
       before = function(self, node)
diff --git a/teal/check/visitors.tl b/teal/check/visitors.tl
index 13d512a3..b14694e0 100644
--- a/teal/check/visitors.tl
+++ b/teal/check/visitors.tl
@@ -1217,7 +1217,14 @@ visit_node.cbs = {
                                     or  "number"
          self:add_var(node.var, node.var.tk, a_type(node.var, typename, {}))
       end,
-      after = end_scope_and_none_type,
+      after = function(self: Context, node: Node, _children: {Type}): Type
+         local var = self:find_var(node.var.tk)
+         if var and var.has_been_written_to then
+            node.fornum_modifies_control_var = true
+         end
+         self:end_scope(node)
+         return NONE
+      end,
    },
    ["return"] = {
       before = function(self: Context, node: Node)
diff --git a/teal/gen/lua_compat.lua b/teal/gen/lua_compat.lua
index e61c0de3..f1550508 100644
--- a/teal/gen/lua_compat.lua
+++ b/teal/gen/lua_compat.lua
@@ -117,6 +117,25 @@ local bit_operators = {
    ["<<"] = "lshift",
 }
 
+
+local function shadow_control_var(node, control_var)
+   if #node.body == 0 then
+      return
+   end
+   local stmt = node_at(node, {
+      kind = "local_declaration",
+      vars = node_at(node, {
+         kind = "variable_list",
+         node_at(node, { kind = "variable", is_lvalue = true, tk = control_var }),
+      }),
+      exps = node_at(node, {
+         kind = "expression_list",
+         node_at(node, { kind = "variable", tk = control_var }),
+      }),
+   })
+   table.insert(node.body, 1, stmt)
+end
+
 local function adjust_code(ast, needs_compat, gen_compat, gen_target)
    local visit = false
 
@@ -246,24 +265,15 @@ local function adjust_code(ast, needs_compat, gen_compat, gen_target)
       visit = true
       visit_node.cbs["forin"] = {
          after = function(_, node, _children)
-            if #node.body == 0 then
-               return
-            end
             if node.forin_modifies_control_var then
-               local control_var = node.vars[1].tk
-               local loc_at = node
-               local stmt = node_at(loc_at, {
-                  kind = "local_declaration",
-                  vars = node_at(loc_at, {
-                     kind = "variable_list",
-                     node_at(loc_at, { kind = "variable", is_lvalue = true, tk = control_var }),
-                  }),
-                  exps = node_at(loc_at, {
-                     kind = "expression_list",
-                     node_at(loc_at, { kind = "variable", tk = control_var }),
-                  }),
-               })
-               table.insert(node.body, 1, stmt)
+               shadow_control_var(node, node.vars[1].tk)
+            end
+         end,
+      }
+      visit_node.cbs["fornum"] = {
+         after = function(_, node, _children)
+            if node.fornum_modifies_control_var then
+               shadow_control_var(node, node.var.tk)
             end
          end,
       }
diff --git a/teal/gen/lua_compat.tl b/teal/gen/lua_compat.tl
index c60750ef..bfadd2a7 100644
--- a/teal/gen/lua_compat.tl
+++ b/teal/gen/lua_compat.tl
@@ -117,6 +117,25 @@ local bit_operators: {string:string} = {
    ["<<"] = "lshift",
 }
 
+-- shadow var function
+local function shadow_control_var(node: Node, control_var: string)
+   if #node.body == 0 then
+      return
+   end
+   local stmt = node_at(node, {
+      kind = "local_declaration",
+      vars = node_at(node, {
+         kind = "variable_list",
+         node_at(node, { kind = "variable", is_lvalue = true, tk = control_var }),
+      }),
+      exps = node_at(node, {
+         kind = "expression_list",
+         node_at(node, { kind = "variable", tk = control_var }),
+      }),
+   })
+   table.insert(node.body, 1, stmt)
+end
+
 local function adjust_code(ast: Node, needs_compat: {string:boolean}, gen_compat: GenCompat, gen_target: string)
    local visit = false
 
@@ -246,24 +265,15 @@ local function adjust_code(ast: Node, needs_compat: {string:boolean}, gen_compat
       visit = true
       visit_node.cbs["forin"] = {
          after = function(_: nil, node: Node, _children: {nil}): nil
-            if #node.body == 0 then
-               return
-            end
             if node.forin_modifies_control_var then
-               local control_var = node.vars[1].tk
-               local loc_at = node
-               local stmt = node_at(loc_at, {
-                  kind = "local_declaration",
-                  vars = node_at(loc_at, {
-                     kind = "variable_list",
-                     node_at(loc_at, { kind = "variable", is_lvalue = true, tk = control_var }),
-                  }),
-                  exps = node_at(loc_at, {
-                     kind = "expression_list",
-                     node_at(loc_at, { kind = "variable", tk = control_var }),
-                  }),
-               })
-               table.insert(node.body, 1, stmt)
+               shadow_control_var(node, node.vars[1].tk)
+            end
+         end,
+      }
+      visit_node.cbs["fornum"] = {
+         after = function(_: nil, node: Node, _children: {nil}): nil
+            if node.fornum_modifies_control_var then
+               shadow_control_var(node, node.var.tk)
             end
          end,
       }
diff --git a/tl.lua b/tl.lua
index 97af5566..08fec085 100644
--- a/tl.lua
+++ b/tl.lua
@@ -490,6 +490,7 @@ local parse_typeargs_if_any
 
 
 
+
 
 
 local ast = {}
@@ -8740,7 +8741,14 @@ visit_node.cbs = {
          "number"
          self:add_var(node.var, node.var.tk, a_type(node.var, typename, {}))
       end,
-      after = end_scope_and_none_type,
+      after = function(self, node, _children)
+         local var = self:find_var(node.var.tk)
+         if var and var.has_been_written_to then
+            node.fornum_modifies_control_var = true
+         end
+         self:end_scope(node)
+         return NONE
+      end,
    },
    ["return"] = {
       before = function(self, node)
@@ -11408,6 +11416,25 @@ local bit_operators = {
    ["<<"] = "lshift",
 }
 
+
+local function shadow_control_var(node, control_var)
+   if #node.body == 0 then
+      return
+   end
+   local stmt = node_at(node, {
+      kind = "local_declaration",
+      vars = node_at(node, {
+         kind = "variable_list",
+         node_at(node, { kind = "variable", is_lvalue = true, tk = control_var }),
+      }),
+      exps = node_at(node, {
+         kind = "expression_list",
+         node_at(node, { kind = "variable", tk = control_var }),
+      }),
+   })
+   table.insert(node.body, 1, stmt)
+end
+
 local function adjust_code(ast, needs_compat, gen_compat, gen_target)
    local visit = false
 
@@ -11537,24 +11564,15 @@ local function adjust_code(ast, needs_compat, gen_compat, gen_target)
       visit = true
       visit_node.cbs["forin"] = {
          after = function(_, node, _children)
-            if #node.body == 0 then
-               return
-            end
             if node.forin_modifies_control_var then
-               local control_var = node.vars[1].tk
-               local loc_at = node
-               local stmt = node_at(loc_at, {
-                  kind = "local_declaration",
-                  vars = node_at(loc_at, {
-                     kind = "variable_list",
-                     node_at(loc_at, { kind = "variable", is_lvalue = true, tk = control_var }),
-                  }),
-                  exps = node_at(loc_at, {
-                     kind = "expression_list",
-                     node_at(loc_at, { kind = "variable", tk = control_var }),
-                  }),
-               })
-               table.insert(node.body, 1, stmt)
+               shadow_control_var(node, node.vars[1].tk)
+            end
+         end,
+      }
+      visit_node.cbs["fornum"] = {
+         after = function(_, node, _children)
+            if node.fornum_modifies_control_var then
+               shadow_control_var(node, node.var.tk)
             end
          end,
       }