diff --git a/lua/pending/config.lua b/lua/pending/config.lua
index b1ab639..6942c1b 100644
--- a/lua/pending/config.lua
+++ b/lua/pending/config.lua
@@ -100,6 +100,7 @@
 ---@field view pending.ViewConfig
 ---@field max_priority? integer
 ---@field sync? pending.SyncConfig
+---@field lock_done? boolean
 ---@field forge? pending.ForgeConfig
 ---@field icons pending.Icons
 
@@ -114,6 +115,7 @@ local defaults = {
   date_syntax = 'due',
   recur_syntax = 'rec',
   someday_date = '9999-12-30',
+  lock_done = true,
   max_priority = 3,
   view = {
     default = 'category',
diff --git a/lua/pending/diff.lua b/lua/pending/diff.lua
index 29c292b..a213584 100644
--- a/lua/pending/diff.lua
+++ b/lua/pending/diff.lua
@@ -1,5 +1,6 @@
 local config = require('pending.config')
 local forge = require('pending.forge')
+local log = require('pending.log')
 local parse = require('pending.parse')
 
 ---@class pending.ParsedEntry
@@ -102,14 +103,91 @@ function M.apply(lines, s, hidden_ids)
   local order_counter = 0
 
   for _, entry in ipairs(parsed) do
-    if entry.type ~= 'task' then
-      goto continue
-    end
+    if entry.type == 'task' then
+      order_counter = order_counter + 1
 
-    order_counter = order_counter + 1
-
-    if entry.id and old_by_id[entry.id] then
-      if seen_ids[entry.id] then
+      if entry.id and old_by_id[entry.id] then
+        if seen_ids[entry.id] then
+          s:add({
+            description = entry.description,
+            category = entry.category,
+            priority = entry.priority,
+            due = entry.due,
+            recur = entry.rec,
+            recur_mode = entry.rec_mode,
+            order = order_counter,
+            _extra = entry.forge_ref and { _forge_ref = entry.forge_ref } or nil,
+          })
+        else
+          seen_ids[entry.id] = true
+          local task = old_by_id[entry.id]
+          if
+            config.get().lock_done
+            and task.status == 'done'
+            and entry.status == 'done'
+          then
+            if task.order ~= order_counter then
+              task.order = order_counter
+              task.modified = now
+            end
+            log.warn('cannot edit done task — toggle status first')
+          else
+            local changed = false
+            if task.description ~= entry.description then
+              task.description = entry.description
+              changed = true
+            end
+            if task.category ~= entry.category then
+              task.category = entry.category
+              changed = true
+            end
+            if entry.priority == 0 and task.priority > 0 then
+              task.priority = 0
+              changed = true
+            elseif entry.priority > 0 and task.priority == 0 then
+              task.priority = entry.priority
+              changed = true
+            end
+            if entry.due ~= nil and task.due ~= entry.due then
+              task.due = entry.due
+              changed = true
+            end
+            if entry.rec ~= nil then
+              if task.recur ~= entry.rec then
+                task.recur = entry.rec
+                changed = true
+              end
+              if task.recur_mode ~= entry.rec_mode then
+                task.recur_mode = entry.rec_mode
+                changed = true
+              end
+            end
+            if entry.forge_ref ~= nil then
+              if not task._extra then
+                task._extra = {}
+              end
+              task._extra._forge_ref = entry.forge_ref
+              changed = true
+            end
+            if entry.status and task.status ~= entry.status then
+              task.status = entry.status
+              if entry.status == 'done' then
+                task['end'] = now
+              else
+                task['end'] = nil
+              end
+              changed = true
+            end
+            if task.order ~= order_counter then
+              task.order = order_counter
+              changed = true
+            end
+            if changed then
+              task.modified = now
+            end
+          end
+        end
+      else
         s:add({
           description = entry.description,
           category = entry.category,
@@ -120,77 +198,8 @@ function M.apply(lines, s, hidden_ids)
           order = order_counter,
           _extra = entry.forge_ref and { _forge_ref = entry.forge_ref } or nil,
         })
-      else
-        seen_ids[entry.id] = true
-        local task = old_by_id[entry.id]
-        local changed = false
-        if task.description ~= entry.description then
-          task.description = entry.description
-          changed = true
-        end
-        if task.category ~= entry.category then
-          task.category = entry.category
-          changed = true
-        end
-        if entry.priority == 0 and task.priority > 0 then
-          task.priority = 0
-          changed = true
-        elseif entry.priority > 0 and task.priority == 0 then
-          task.priority = entry.priority
-          changed = true
-        end
-        if entry.due ~= nil and task.due ~= entry.due then
-          task.due = entry.due
-          changed = true
-        end
-        if entry.rec ~= nil then
-          if task.recur ~= entry.rec then
-            task.recur = entry.rec
-            changed = true
-          end
-          if task.recur_mode ~= entry.rec_mode then
-            task.recur_mode = entry.rec_mode
-            changed = true
-          end
-        end
-        if entry.forge_ref ~= nil then
-          if not task._extra then
-            task._extra = {}
-          end
-          task._extra._forge_ref = entry.forge_ref
-          changed = true
-        end
-        if entry.status and task.status ~= entry.status then
-          task.status = entry.status
-          if entry.status == 'done' then
-            task['end'] = now
-          else
-            task['end'] = nil
-          end
-          changed = true
-        end
-        if task.order ~= order_counter then
-          task.order = order_counter
-          changed = true
-        end
-        if changed then
-          task.modified = now
-        end
       end
-    else
-      s:add({
-        description = entry.description,
-        category = entry.category,
-        priority = entry.priority,
-        due = entry.due,
-        recur = entry.rec,
-        recur_mode = entry.rec_mode,
-        order = order_counter,
-        _extra = entry.forge_ref and { _forge_ref = entry.forge_ref } or nil,
-      })
     end
-
-    ::continue::
   end
 
   for id, task in pairs(old_by_id) do
diff --git a/spec/diff_spec.lua b/spec/diff_spec.lua
index 01d8aac..c897df1 100644
--- a/spec/diff_spec.lua
+++ b/spec/diff_spec.lua
@@ -287,5 +287,66 @@ describe('diff', function()
       local task = s:get(1)
       assert.are.equal(0, task.priority)
     end)
+
+    it('rejects editing description of a done task', function()
+      local t = s:add({ description = 'Finished work', status = 'done' })
+      t['end'] = '2026-03-01T00:00:00Z'
+      s:save()
+      local lines = {
+        '# Todo',
+        '/1/- [x] Changed description',
+      }
+      diff.apply(lines, s)
+      s:load()
+      local task = s:get(1)
+      assert.are.equal('Finished work', task.description)
+      assert.are.equal('done', task.status)
+    end)
+
+    it('allows toggling done task back to pending', function()
+      local t = s:add({ description = 'Finished work', status = 'done' })
+      t['end'] = '2026-03-01T00:00:00Z'
+      s:save()
+      local lines = {
+        '# Todo',
+        '/1/- [ ] Finished work',
+      }
+      diff.apply(lines, s)
+      s:load()
+      local task = s:get(1)
+      assert.are.equal('pending', task.status)
+    end)
+
+    it('allows editing done task when lock_done is false', function()
+      local cfg = require('pending.config')
+      vim.g.pending = { lock_done = false }
+      cfg.reset()
+      local t = s:add({ description = 'Finished work', status = 'done' })
+      t['end'] = '2026-03-01T00:00:00Z'
+      s:save()
+      local lines = {
+        '# Todo',
+        '/1/- [x] Changed description',
+      }
+      diff.apply(lines, s)
+      s:load()
+      local task = s:get(1)
+      assert.are.equal('Changed description', task.description)
+      vim.g.pending = {}
+      cfg.reset()
+    end)
+
+    it('does not affect editing of pending tasks', function()
+      s:add({ description = 'Active task' })
+      s:save()
+      local lines = {
+        '# Todo',
+        '/1/- [ ] Updated active task',
+      }
+      diff.apply(lines, s)
+      s:load()
+      local task = s:get(1)
+      assert.are.equal('Updated active task', task.description)
+    end)
   end)
 end)