diff --git a/src/luacheck/fs.lua b/src/luacheck/fs.lua
index 101e6a1f..cf95b56c 100644
--- a/src/luacheck/fs.lua
+++ b/src/luacheck/fs.lua
@@ -193,6 +193,13 @@ local function make_absolute_dirs(dir_path)
 
    local make_ok, make_error = lfs.mkdir(dir_path)
 
+   -- Avoid race condition. Even if the mkdir returns an error it *may* be
+   -- because another thread created it in the mean time. If it exists now we
+   -- are good to move on and ignore the error.
+   if fs.is_dir(dir_path) then
+      return true
+   end
+
    if not make_ok then
       return nil, ("Couldn't make directory %s: %s"):format(dir_path, make_error)
    end
diff --git a/src/luacheck/stages/unwrap_parens.lua b/src/luacheck/stages/unwrap_parens.lua
index d790a27f..6d9a82bd 100644
--- a/src/luacheck/stages/unwrap_parens.lua
+++ b/src/luacheck/stages/unwrap_parens.lua
@@ -26,11 +26,9 @@ local replacements = {
    le = ">",
 }
 
-local chstate
-
 -- Mutates an array of nodes and non-tables, unwrapping Paren nodes.
 -- If list_start is given, tail Paren is not unwrapped if it's unpacking and past list_start index.
-local function handle_nodes(nodes, list_start)
+local function handle_nodes(chstate, nodes, list_start)
    local num_nodes = #nodes
 
    for index = 1, num_nodes do
@@ -40,21 +38,21 @@ local function handle_nodes(nodes, list_start)
          local tag = node.tag
 
          if tag == "Table" or tag == "Return" then
-            handle_nodes(node, 1)
+            handle_nodes(chstate, node, 1)
          elseif tag == "Call" then
-            handle_nodes(node, 2)
+            handle_nodes(chstate, node, 2)
          elseif tag == "Invoke" then
-            handle_nodes(node, 3)
+            handle_nodes(chstate, node, 3)
          elseif tag == "Forin" then
-            handle_nodes(node[2], 1)
-            handle_nodes(node[3])
+            handle_nodes(chstate, node[2], 1)
+            handle_nodes(chstate, node[3])
          elseif tag == "Local" then
             if node[2] then
-               handle_nodes(node[2])
+               handle_nodes(chstate, node[2])
             end
          elseif tag == "Set" then
-            handle_nodes(node[1])
-            handle_nodes(node[2], 1)
+            handle_nodes(chstate, node[1])
+            handle_nodes(chstate, node[2], 1)
          else
             -- warn that not x == y means (not x) == y
             if tag ~= "Paren"
@@ -66,11 +64,11 @@ local function handle_nodes(nodes, list_start)
                chstate:warn_range("582", node[1])
             end
 
-            handle_nodes(node)
+            handle_nodes(chstate, node)
 
             -- warn that not (x == y) can become x ~= y
             if tag == "Op" and node[1] == "not" and node[2].tag == "Op" and relational_operators[node[2][1]] then
-               chstate:warn_range("581", node, {
+            chstate:warn_range("581", node, {
                   operator = relational_operators[node[2][1]],
                   replacement_operator = replacements[node[2][1]]
                })
@@ -91,9 +89,8 @@ end
 -- Mutates AST, unwrapping Paren nodes.
 -- Paren nodes are preserved only when they matter:
 -- at the ends of expression lists with potentially multi-value inner expressions.
-function stage.run(check_state)
-   chstate = check_state
-   handle_nodes(check_state.ast)
+function stage.run(chstate)
+   handle_nodes(chstate, chstate.ast)
 end
 
 return stage