diff --git a/backend/app/controllers/wiki_pages_controller.rb b/backend/app/controllers/wiki_pages_controller.rb
index 4943fbf..fb465a3 100644
--- a/backend/app/controllers/wiki_pages_controller.rb
+++ b/backend/app/controllers/wiki_pages_controller.rb
@@ -31,17 +31,20 @@ class WikiPagesController < ApplicationController
 
   def diff
     id = params[:id]
-    from = params[:from]
+    return head :bad_request if id.blank?
+
+    from = params[:from].presence
     to = params[:to].presence
-    return head :bad_request if id.blank? || from.blank?
 
     page = WikiPage.find(id)
 
-    from_rev = page.wiki_revisions.find(from)
+    from_rev = from && page.wiki_revisions.find(from)
     to_rev = to ? page.wiki_revisions.find(to) : page.current_revision
-    return head :unprocessable_entity if !(from_rev&.content?) || !(to_rev&.content?)
+    if ((from_rev && !(from_rev.content?)) || !(to_rev&.content?))
+      return head :unprocessable_entity
+    end
 
-    diffs = Diff::LCS.sdiff(from_rev.body.lines, to_rev.body.lines)
+    diffs = Diff::LCS.sdiff(from_rev&.body&.lines || [], to_rev.body.lines)
     diff_json = diffs.map { |change|
       case change.action
       when ?=
@@ -58,7 +61,7 @@ class WikiPagesController < ApplicationController
 
     render json: { wiki_page_id:      page.id,
                    title:             page.title,
-                   older_revision_id: from_rev.id,
+                   older_revision_id: from_rev&.id,
                    newer_revision_id: to_rev.id,
                    diff:              diff_json }
   end
diff --git a/backend/app/models/wiki_line.rb b/backend/app/models/wiki_line.rb
index 7a1b4e2..c169917 100644
--- a/backend/app/models/wiki_line.rb
+++ b/backend/app/models/wiki_line.rb
@@ -8,7 +8,7 @@ class WikiLine < ApplicationRecord
     sha = Digest::SHA256.hexdigest(body)
     now = Time.current
 
-    upsert({ sha256: sha, body:, created_at: now, updated_at: now }, unique_by: :sha256)
+    upsert({ sha256: sha, body:, created_at: now, updated_at: now })
 
     find_by!(sha256: sha)
   end
diff --git a/backend/lib/tasks/migrate_wiki.rake b/backend/lib/tasks/migrate_wiki.rake
new file mode 100644
index 0000000..1fd7ad1
--- /dev/null
+++ b/backend/lib/tasks/migrate_wiki.rake
@@ -0,0 +1,73 @@
+namespace :wiki do
+  desc 'Wiki 移行'
+  task migrate: :environment do
+    require 'digest'
+    require 'gollum-lib'
+
+    wiki = Gollum::Wiki.new(Rails.root.join('wiki').to_s)
+
+    WikiPage.where.missing(:wiki_revisions).find_each do |wiki_page|
+      page = wiki.page("#{ wiki_page.id }.md")
+      next unless page
+
+      versions = page.versions
+      next if versions.blank?
+
+      base_revision_id = nil
+      versions.reverse_each do |version|
+        pg = wiki.page("#{ wiki_page.id }.md", version.id)
+        raw = pg&.raw_data
+        next unless raw
+
+        lines = raw.force_encoding('UTF-8').split("\n")
+
+        line_shas = lines.map { |l| Digest::SHA256.hexdigest(l) }
+        tree_sha = Digest::SHA256.hexdigest(line_shas.join(','))
+
+        at = version.authored_date
+
+        line_id_by_sha = WikiLine.where(sha256: line_shas).pluck(:sha256, :id).to_h
+
+        missing_rows = []
+        line_shas.each_with_index do |sha, i|
+          next if line_id_by_sha.key?(sha)
+
+          missing_rows << { sha256:     sha,
+                            body:       lines[i],
+                            created_at: at,
+                            updated_at: at }
+        end
+
+        if missing_rows.any?
+          WikiLine.upsert_all(missing_rows)
+          line_id_by_sha = WikiLine.where(sha256: line_shas).pluck(:sha256, :id).to_h
+        end
+        line_ids = line_shas.map { |sha| line_id_by_sha.fetch(sha) }
+
+        ActiveRecord::Base.transaction do
+          wiki_page.lock!
+
+          rev = WikiRevision.create!(
+              wiki_page:,
+              base_revision_id:,
+              created_user_id:  Integer(version.author.name) rescue 2,
+              kind:             :content,
+              redirect_page_id: nil,
+              message:          nil,
+              lines_count:      lines.length,
+              tree_sha256:      tree_sha,
+              created_at:       at,
+              updated_at:       at)
+
+          rows = line_ids.each_with_index.map do |line_id, pos|
+            { wiki_revision_id: rev.id,
+              wiki_line_id:     line_id,
+              position:         pos }
+          end
+          WikiRevisionLine.insert_all!(rows)
+        end
+        base_revision_id = rev.id
+      end
+    end
+  end
+end
diff --git a/frontend/src/types.ts b/frontend/src/types.ts
index 46cacce..0dccb59 100644
--- a/frontend/src/types.ts
+++ b/frontend/src/types.ts
@@ -84,7 +84,7 @@ export type WikiPageDiff = {
     wikiPageId:       number
     title:            string
     olderRevisionId:  number | null
-    newerRevisionId:  number | null
+    newerRevisionId:  number
     diff:             WikiPageDiffDiff[] }
 
 export type WikiPageDiffDiff = {