diff --git a/changelog.txt b/changelog.txt
index 1ed30ae501..412720dc1b 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -34,6 +34,7 @@ Template for new versions:
 
 ## Fixes
 - `bodyswap`: fix "invalid argument count" when the target unit has no nemesis record
+- `gui/settings-manager`: preserve built-in work details added after saved settings were created
 - `fix/loyaltycascade`: guard against citizens that are not historical figures and emit a warning.
 - `gui/siegemanager`: fix nil index if there are no siege engines on the map
 
diff --git a/gui/settings-manager.lua b/gui/settings-manager.lua
index 140310c2e4..95fae65f9d 100644
--- a/gui/settings-manager.lua
+++ b/gui/settings-manager.lua
@@ -516,22 +516,53 @@ local function save_work_details()
     config:write()
 end
 
+local function apply_work_detail(detail, wd)
+    local flags = wd.flags or wd.work_detail_flags -- compat for old name
+    detail.name = wd.name
+    detail.icon = wd.icon
+    detail.flags.cannot_be_everybody = flags.cannot_be_everybody
+    detail.flags.no_modify = flags.no_modify
+    detail.flags.mode = flags.mode
+    for i,v in ipairs(wd.allowed_labors) do
+        detail.allowed_labors[i-1] = v
+    end
+end
+
 local function load_work_details()
     if not config.data.work_details or #config.data.work_details < 10 then
         -- not enough data to cover built-in work details
         return
     end
-    li.work_details:resize(#config.data.work_details)
-    -- keep unit assignments for overwritten indices
-    for idx, wd in ipairs(config.data.work_details) do
-        local detail = {
+
+    local saved_builtins, saved_custom = {}, {}
+    for _,wd in ipairs(config.data.work_details) do
+        local flags = wd.flags or wd.work_detail_flags
+        if flags.no_modify then
+            saved_builtins[('%s\0%s'):format(wd.icon, wd.name)] = wd
+        else
+            table.insert(saved_custom, wd)
+        end
+    end
+
+    local builtin_count = 0
+    for idx = 0, #li.work_details - 1 do
+        local detail = li.work_details[idx]
+        if not detail.flags.no_modify then break end
+        builtin_count = builtin_count + 1
+        local wd = saved_builtins[('%s\0%s'):format(detail.icon, detail.name)]
+        if wd then apply_work_detail(detail, wd) end
+    end
+
+    li.work_details:resize(builtin_count + #saved_custom)
+    for idx,wd in ipairs(saved_custom) do
+        local detail_idx = builtin_count + idx - 1
+        li.work_details[detail_idx] = {
             new=df.work_detail,
             name=wd.name,
             icon=wd.icon,
-            flags=wd.flags or wd.work_detail_flags, -- compat for old name
+            flags=wd.flags or wd.work_detail_flags,
         }
-        li.work_details[idx-1] = detail
-        local al = li.work_details[idx-1].allowed_labors
+        local al = li.work_details[detail_idx].allowed_labors
         for i,v in ipairs(wd.allowed_labors) do
             al[i-1] = v
         end
diff --git a/test/gui/settings-manager.lua b/test/gui/settings-manager.lua
new file mode 100644
index 0000000000..e4263d0088
--- /dev/null
+++ b/test/gui/settings-manager.lua
@@ -0,0 +1,129 @@
+config = {
+    mode = 'fortress',
+    target = 'gui/settings-manager',
+}
+
+local settings_manager = reqscript('gui/settings-manager')
+
+local function make_vector(entries)
+    local data = entries or {}
+    return setmetatable({}, {
+        __len=function() return #data end,
+        __index=function(_, key)
+            if key == 'resize' then
+                return function(_, size)
+                    for i = #data, size - 1 do data[i+1] = false end
+                    for i = #data, size + 1, -1 do data[i] = nil end
+                end
+            end
+            return type(key) == 'number' and data[key+1] or nil
+        end,
+        __newindex=function(_, key, value)
+            if type(key) ~= 'number' then return end
+            if type(value) == 'table' and value.new == df.work_detail then
+                value = {
+                    name=value.name,
+                    icon=value.icon,
+                    flags=value.flags,
+                    allowed_labors={},
+                }
+            end
+            data[key+1] = value
+        end,
+    })
+end
+
+local function with_work_details(work_details, saved, fn)
+    local load_fn = settings_manager.WorkDetailsOverlay.ATTRS.load_fn
+    local li_idx, old_li
+    for i = 1, 10 do
+        local name, value = debug.getupvalue(load_fn, i)
+        if name == 'li' then
+            li_idx, old_li = i, value
+            break
+        end
+    end
+    local old_config = settings_manager.config
+    debug.setupvalue(load_fn, li_idx, {work_details=work_details})
+    settings_manager.config = {data={work_details=saved}, write=function() end}
+    dfhack.with_finalize(
+        function()
+            debug.setupvalue(load_fn, li_idx, old_li)
+            settings_manager.config = old_config
+        end,
+        function() fn(load_fn) end)
+end
+
+local function saved_detail(index)
+    return {
+        name=('built-in %d'):format(index),
+        icon=index,
+        flags={cannot_be_everybody=false, no_modify=true, mode=1},
+        allowed_labors={},
+    }
+end
+
+local function current_details()
+    local current = {}
+    for i = 1, 10 do current[i] = saved_detail(i) end
+    current[11] = {
+        name='Siege Operators',
+        icon=df.work_detail_icon_type.SIEGE_OPERATORS,
+        flags={cannot_be_everybody=false, no_modify=true, mode=1},
+        allowed_labors={},
+    }
+    return current
+end
+
+function test.loading_old_details_preserves_new_builtin()
+    local saved = {}
+    for i = 1, 10 do saved[i] = saved_detail(i) end
+    local work_details = make_vector(current_details())
+
+    with_work_details(work_details, saved, function(load_fn)
+        load_fn()
+        expect.eq(11, #work_details)
+        if #work_details < 11 then return end
+        expect.eq('Siege Operators', work_details[10].name)
+    end)
+end
+
+function test.loading_legacy_work_detail_flags()
+    local saved = {}
+    for i = 1, 10 do saved[i] = saved_detail(i) end
+    saved[1].work_detail_flags = saved[1].flags
+    saved[1].flags = nil
+    saved[1].work_detail_flags.mode = 3
+    local work_details = make_vector(current_details())
+
+    with_work_details(work_details, saved, function(load_fn)
+        load_fn()
+        expect.eq(3, work_details[0].flags.mode)
+    end)
+end
+
+function test.loading_old_custom_details_after_new_builtins()
+    local saved = {}
+    for i = 1, 10 do saved[i] = saved_detail(i) end
+    saved[11] = {
+        name='Custom detail',
+        icon=1,
+        flags={cannot_be_everybody=false, no_modify=false, mode=1},
+        allowed_labors={},
+    }
+    local current = current_details()
+    current[12] = {
+        name='Unsaved custom detail',
+        icon=2,
+        flags={cannot_be_everybody=false, no_modify=false, mode=1},
+        allowed_labors={},
+    }
+    local work_details = make_vector(current)
+
+    with_work_details(work_details, saved, function(load_fn)
+        load_fn()
+        expect.eq(12, #work_details)
+        expect.eq('Siege Operators', work_details[10].name)
+        expect.eq('Custom detail', work_details[11].name)
+    end)
+end