diff --git a/lib/gears/cache.lua b/lib/gears/cache.lua
index 7329a1e7..905f58b0 100644
--- a/lib/gears/cache.lua
+++ b/lib/gears/cache.lua
@@ -7,7 +7,7 @@
 
 local select = select
 local setmetatable = setmetatable
-local unpack = unpack or table.unpack
+local unpack = unpack or table.unpack -- luacheck: globals unpack (compatibility with Lua 5.1)
 
 local cache = {}
 
diff --git a/lib/gears/color.lua b/lib/gears/color.lua
index 63533c48..5454dfc3 100644
--- a/lib/gears/color.lua
+++ b/lib/gears/color.lua
@@ -8,7 +8,7 @@
 local setmetatable = setmetatable
 local string = string
 local table = table
-local unpack = unpack or table.unpack -- v5.1: unpack, v5.2: table.unpack
+local unpack = unpack or table.unpack -- luacheck: globals unpack (compatibility with Lua 5.1)
 local tonumber = tonumber
 local ipairs = ipairs
 local pairs = pairs
@@ -88,7 +88,6 @@ end
 -- @param col The color for the pattern
 -- @return A cairo pattern object
 function color.create_solid_pattern(col)
-    local col = col
     if col == nil then
         col = "#000000"
     elseif type(col) == "table" then
@@ -102,7 +101,6 @@ end
 -- @param file The filename of the file
 -- @return a cairo pattern object
 function color.create_png_pattern(file)
-    local file = file
     if type(file) == "table" then
         file = file.file
     end
@@ -138,7 +136,7 @@ local function string_pattern(creator, arg)
     local args = { parse_numbers(iterator()) }
     local to = { parse_numbers(iterator()) }
     -- Now merge those two tables
-    for k, v in pairs(to) do
+    for _, v in pairs(to) do
         table.insert(args, v)
     end
     -- And call our creator function with the values
@@ -220,7 +218,7 @@ function color.create_pattern_uncached(col)
     if cairo.Pattern:is_type_of(col) then
         return col
     end
-    local col = col or "#000000"
+    col = col or "#000000"
     if type(col) == "string" then
         local t = string.match(col, "[^:]+")
         if color.types[t] then
@@ -271,18 +269,17 @@ end
 -- @return The pattern if it is surely opaque, else nil
 function color.create_opaque_pattern(col)
     local pattern = color.create_pattern(col)
-    local type = pattern:get_type()
-    local extend = pattern:get_extend()
+    local kind = pattern:get_type()
 
-    if type == "SOLID" then
-        local status, r, g, b, a = pattern:get_rgba()
-        if a ~= 1 then
+    if kind == "SOLID" then
+        local _, _, _, _, alpha = pattern:get_rgba()
+        if alpha ~= 1 then
             return
         end
         return pattern
-    elseif type == "SURFACE" then
-        local status, surface = pattern:get_surface()
-        if status ~= "SUCCESS" or surface.content ~= "COLOR" then
+    elseif kind == "SURFACE" then
+        local status, surf = pattern:get_surface()
+        if status ~= "SUCCESS" or surf.content ~= "COLOR" then
             -- The surface has an alpha channel which *might* be non-opaque
             return
         end
@@ -294,8 +291,8 @@ function color.create_opaque_pattern(col)
         end
 
         return pattern
-    elseif type == "LINEAR" then
-        local status, stops = pattern:get_color_stop_count()
+    elseif kind == "LINEAR" then
+        local _, stops = pattern:get_color_stop_count()
 
         -- No color stops or extend NONE -> pattern *might* contain transparency
         if stops == 0 or pattern:get_extend() == "NONE" then
@@ -304,8 +301,8 @@ function color.create_opaque_pattern(col)
 
         -- Now check if any of the color stops contain transparency
         for i = 0, stops - 1 do
-            local status, offset, r, g, b, a = pattern:get_color_stop_rgba(i)
-            if a ~= 1 then
+            local _, _, _, _, _, alpha = pattern:get_color_stop_rgba(i)
+            if alpha ~= 1 then
                 return
             end
         end
@@ -330,7 +327,7 @@ function color.recolor_image(image, new_color)
     return image
 end
 
-function color.mt:__call(...)
+function color.mt.__call(_, ...)
     return color.create_pattern(...)
 end
 
diff --git a/lib/gears/debug.lua b/lib/gears/debug.lua
index af323e2e..ec27ed5d 100644
--- a/lib/gears/debug.lua
+++ b/lib/gears/debug.lua
@@ -5,9 +5,7 @@
 -- @module gears.debug
 ---------------------------------------------------------------------------
 
-local error = error
 local tostring = tostring
-local traceback = debug.traceback
 local print = print
 local type = type
 local pairs = pairs
diff --git a/lib/gears/matrix.lua b/lib/gears/matrix.lua
index 687a4f96..ed91915e 100644
--- a/lib/gears/matrix.lua
+++ b/lib/gears/matrix.lua
@@ -175,7 +175,7 @@ end
 -- @treturn number The x coordinate of the transformed point.
 -- @treturn number The x coordinate of the transformed point.
 function matrix:transform_point(x, y)
-    local x, y = self:transform_distance(x, y)
+    x, y = self:transform_distance(x, y)
     return self.x0 + x, self.y0 + y
 end
 
@@ -195,10 +195,10 @@ function matrix:transform_rectangle(x, y, width, height)
     local x3, y3 = self:transform_point(x + width, y + height)
     local x4, y4 = self:transform_point(x + width, y)
     -- Find the extremal points of the result
-    local x = math.min(x1, x2, x3, x4)
-    local y = math.min(y1, y2, y3, y4)
-    local width = math.max(x1, x2, x3, x4) - x
-    local height = math.max(y1, y2, y3, y4) - y
+    x = math.min(x1, x2, x3, x4)
+    y = math.min(y1, y2, y3, y4)
+    width = math.max(x1, x2, x3, x4) - x
+    height = math.max(y1, y2, y3, y4) - y
 
     return x, y, width, height
 end
diff --git a/lib/gears/object.lua b/lib/gears/object.lua
index e2f9ef02..2eb230cd 100644
--- a/lib/gears/object.lua
+++ b/lib/gears/object.lua
@@ -60,6 +60,7 @@ local function make_the_gc_obey(func)
         -- Lua 5.1 only has the behaviour we want if a userdata is used as the
         -- value in a weak table. Thus, do some magic so that we get a userdata.
 
+        -- luacheck: globals newproxy getfenv setfenv
         local userdata = newproxy(true)
         getmetatable(userdata).__gc = function() end
         -- Now bind the lifetime of userdata to the lifetime of func. For this,
@@ -137,7 +138,7 @@ local function new()
     return ret
 end
 
-function object.mt:__call(...)
+function object.mt.__call(_, ...)
     return new(...)
 end
 
diff --git a/lib/gears/shape.lua b/lib/gears/shape.lua
index 76b16f87..eff81489 100644
--- a/lib/gears/shape.lua
+++ b/lib/gears/shape.lua
@@ -64,9 +64,9 @@ end
 -- @tparam[opt=10] number arrow_size The width and height of the arrow
 -- @tparam[opt=width/2 - arrow_size/2] number arrow_position The position of the arrow
 function module.infobubble(cr, width, height, corner_radius, arrow_size, arrow_position)
-    local corner_radius  = corner_radius  or 5
-    local arrow_size     = arrow_size     or 10
-    local arrow_position = arrow_position or width/2 - arrow_size/2
+    corner_radius  = corner_radius  or 5
+    arrow_size     = arrow_size     or 10
+    arrow_position = arrow_position or width/2 - arrow_size/2
 
     cr:move_to(0 ,corner_radius)
 
@@ -109,9 +109,9 @@ end
 -- @tparam[opt=width /2] number shaft_width The width of the shaft of the arrow
 -- @tparam[opt=height/2] number shaft_length The head_length of the shaft (the rest is the head)
 function module.arrow(cr, width, height, head_width, shaft_width, shaft_length)
-    local shaft_length = shaft_length or height / 2
-    local shaft_width  = shaft_width  or width  / 2
-    local head_width   = head_width   or width
+    shaft_length = shaft_length or height / 2
+    shaft_width  = shaft_width  or width  / 2
+    head_width   = head_width   or width
     local head_length  = height - shaft_length
 
     cr:move_to    ( width/2                     , 0            )
@@ -146,7 +146,7 @@ end
 -- @tparam number height The shape height
 -- @tparam[opt=height/2] number arrow_depth The width of the arrow part of the shape
 function module.powerline(cr, width, height, arrow_depth)
-    local arrow_depth = arrow_depth or height/2
+    arrow_depth = arrow_depth or height/2
     cr:move_to(0                   , 0        )
     cr:line_to(width - arrow_depth , 0        )
     cr:line_to(width               , height/2 )
diff --git a/lib/gears/surface.lua b/lib/gears/surface.lua
index 64afabea..ed9e7b9c 100644
--- a/lib/gears/surface.lua
+++ b/lib/gears/surface.lua
@@ -114,7 +114,7 @@ function surface.load(_surface)
     return do_load_and_handle_errors(_surface, surface.load_silently)
 end
 
-function surface.mt:__call(...)
+function surface.mt.__call(_, ...)
     return surface.load(...)
 end
 
diff --git a/lib/gears/timer.lua b/lib/gears/timer.lua
index 6eee64be..1c50cefe 100644
--- a/lib/gears/timer.lua
+++ b/lib/gears/timer.lua
@@ -14,7 +14,7 @@ local setmetatable = setmetatable
 local table = table
 local tonumber = tonumber
 local traceback = debug.traceback
-local unpack = unpack or table.unpack -- v5.1: unpack, v5.2: table.unpack
+local unpack = unpack or table.unpack -- luacheck: globals unpack (compatibility with Lua 5.1)
 local glib = require("lgi").GLib
 local object = require("gears.object")
 
@@ -43,7 +43,7 @@ function timer:start()
         return
     end
     self.data.source_id = glib.timeout_add(glib.PRIORITY_DEFAULT, self.data.timeout * 1000, function()
-        local success, message = xpcall(function()
+        xpcall(function()
                 self:emit_signal("timeout")
             end, function(err)
                 print(debug.traceback("Error during executing timeout handler: "..tostring(err)))
@@ -160,7 +160,7 @@ end
 local delayed_calls = {}
 capi.awesome.connect_signal("refresh", function()
     for _, callback in ipairs(delayed_calls) do
-        local success, message = xpcall(function()
+        xpcall(function()
                 callback[1](unpack(callback, 2))
             end, function(err)
                 print(debug.traceback("Error during delayed call: "..tostring(err), 2))
@@ -177,7 +177,7 @@ function timer.delayed_call(callback, ...)
     table.insert(delayed_calls, { callback, ... })
 end
 
-function timer.mt:__call(...)
+function timer.mt.__call(_, ...)
     return timer.new(...)
 end
 
diff --git a/lib/gears/wallpaper.lua b/lib/gears/wallpaper.lua
index e09262a9..aba2464e 100644
--- a/lib/gears/wallpaper.lua
+++ b/lib/gears/wallpaper.lua
@@ -58,9 +58,9 @@ function wallpaper.prepare_context(s)
 
         -- Set the wallpaper (delayed)
         timer.delayed_call(function()
-            local wp = pending_wallpaper
+            local paper = pending_wallpaper
             pending_wallpaper = nil
-            wallpaper.set(wp)
+            wallpaper.set(paper)
         end)
     else
         -- Draw to the already-pending wallpaper
@@ -99,8 +99,8 @@ end
 --   gears.color. The default is black.
 function wallpaper.centered(surf, s, background)
     local geom, cr = wallpaper.prepare_context(s)
-    local surf = surface(surf)
-    local background = color(background)
+    surf = surface(surf)
+    background = color(background)
 
     -- Fill the area with the background
     cr.operator = cairo.Operator.SOURCE
@@ -122,7 +122,7 @@ end
 --   all screens are set.
 -- @param offset This can be set to a table with entries x and y.
 function wallpaper.tiled(surf, s, offset)
-    local geom, cr = wallpaper.prepare_context(s)
+    local _, cr = wallpaper.prepare_context(s)
 
     if offset then
         cr:translate(offset.x, offset.y)
@@ -144,7 +144,7 @@ end
 -- @param offset This can be set to a table with entries x and y.
 function wallpaper.maximized(surf, s, ignore_aspect, offset)
     local geom, cr = wallpaper.prepare_context(s)
-    local surf = surface(surf)
+    surf = surface(surf)
     local w, h = surface.get_size(surf)
     local aspect_w = geom.width / w
     local aspect_h = geom.height / h
@@ -176,8 +176,8 @@ end
 --   gears.color. The default is black.
 function wallpaper.fit(surf, s, background)
     local geom, cr = wallpaper.prepare_context(s)
-    local surf = surface(surf)
-    local background = color(background)
+    surf = surface(surf)
+    background = color(background)
 
     -- Fill the area with the background
     cr.operator = cairo.Operator.SOURCE