diff --git a/lib/naughty/constants.lua b/lib/naughty/constants.lua
index ce237b13..d1f5157d 100644
--- a/lib/naughty/constants.lua
+++ b/lib/naughty/constants.lua
@@ -9,9 +9,10 @@
 -- @copyright 2017 Emmanuel Lepage Vallee
 ----------------------------------------------------------------------------
 local beautiful = require("beautiful")
+local gtable = require("gears.table")
 local dpi = beautiful.xresources.apply_dpi
 
-local ret = {}
+local ret, no_clear = {}, {}
 
 ret.config = {
     padding         = dpi(4),
@@ -21,7 +22,7 @@ ret.config = {
     notify_callback = nil,
 }
 
-ret.config.presets = {
+no_clear.presets = {
     low = {
         timeout = 5
     },
@@ -55,15 +56,15 @@ ret.config._urgency = {
 }
 
 ret.config.mapping = {
-    {{urgency = ret.config._urgency.low     }, ret.config.presets.low}, --compat
-    {{urgency = ret.config._urgency.normal  }, ret.config.presets.normal}, --compat
-    {{urgency = ret.config._urgency.critical}, ret.config.presets.critical}, --compat
-    {{urgency = "low"     }, ret.config.presets.low},
-    {{urgency = "normal"  }, ret.config.presets.normal},
-    {{urgency = "critical"}, ret.config.presets.critical},
+    {{urgency = ret.config._urgency.low     }, no_clear.presets.low}, --compat
+    {{urgency = ret.config._urgency.normal  }, no_clear.presets.normal}, --compat
+    {{urgency = ret.config._urgency.critical}, no_clear.presets.critical}, --compat
+    {{urgency = "low"     }, no_clear.presets.low},
+    {{urgency = "normal"  }, no_clear.presets.normal},
+    {{urgency = "critical"}, no_clear.presets.critical},
 }
 
-ret.config.defaults = {
+no_clear.defaults = {
     timeout      = 5,
     text         = "",
     screen       = nil,
@@ -92,4 +93,21 @@ ret.notification_closed_reason = {
 -- Legacy --TODO v5 remove this alias
 ret.notificationClosedReason = ret.notification_closed_reason
 
+-- `no_clear` is used to prevent users from setting the entire table.
+-- If they did and we added a new default value, then it would not be
+-- backward compatible. For safety, we just crush the tables rather than
+-- replace them.
+setmetatable(ret.config, {
+    __index = function(_, key)
+        return no_clear[key]
+    end,
+    __newindex = function(_, key, value)
+        if no_clear[key] then
+            gtable.crush(no_clear[key], value)
+        else
+            rawset(ret.config, key, value)
+        end
+    end
+})
+
 return ret
diff --git a/tests/test-naughty-legacy.lua b/tests/test-naughty-legacy.lua
index 86c992ee..7d716e37 100644
--- a/tests/test-naughty-legacy.lua
+++ b/tests/test-naughty-legacy.lua
@@ -1256,4 +1256,15 @@ table.insert(steps, function()
     return true
 end)
 
+-- Make sure it isn't possible to remove default variables (#3145).
+table.insert(steps, function()
+    naughty.config.defaults = {fake_variable = 24}
+    naughty.config.text = 1337
+    assert(naughty.config.defaults.fake_variable == 24)
+    assert(naughty.config.defaults.timeout == 5)
+    assert(naughty.config.text == 1337)
+
+     return true
+end)
+
 require("_runner").run_steps(steps)