diff --git a/extensions/general/arcim-migration/__tests__/mapping-targets.test.ts b/extensions/general/arcim-migration/__tests__/mapping-targets.test.ts
new file mode 100644
index 00000000..5c5adce7
--- /dev/null
+++ b/extensions/general/arcim-migration/__tests__/mapping-targets.test.ts
@@ -0,0 +1,82 @@
+import { describe, expect, it } from 'vitest'
+import type { SupabaseClient } from '@supabase/supabase-js'
+
+import { buildMappingTargets } from '../lib/mapping-targets'
+
+/**
+ * A chart_of_accounts read that returns the given rows for any range, which is
+ * all fetchAllRows needs: one page, then an empty one.
+ */
+function supabaseWith(rows: Array<Record<string, unknown>> | Error): SupabaseClient {
+  let served = false
+  const range = () =>
+    rows instanceof Error
+      ? Promise.resolve({ data: null, error: { message: rows.message } })
+      : Promise.resolve({ data: served ? [] : ((served = true), rows), error: null })
+  const builder = {
+    select: () => builder,
+    eq: () => builder,
+    order: () => builder,
+    range,
+  }
+  return { from: () => builder } as unknown as SupabaseClient
+}
+
+describe('buildMappingTargets', () => {
+  // The bug this file exists for: BAS defines 3000-3004 and stops, so a
+  // company account like 3005 was active in the chart, visible everywhere else
+  // in the app, and still absent from the migration's mapping dropdown.
+  it('offers a company account that BAS does not define', async () => {
+    const targets = await buildMappingTargets(
+      supabaseWith([
+        { account_number: '3005', account_name: 'Provisioner inom Sverige', account_class: 3 },
+      ]),
+      'company-1',
+    )
+    const found = targets.find((t) => t.account_number === '3005')
+    expect(found?.account_name).toBe('Provisioner inom Sverige')
+  })
+
+  it('still offers standard accounts the company has not created', async () => {
+    const targets = await buildMappingTargets(supabaseWith([]), 'company-1')
+    expect(targets.find((t) => t.account_number === '1930')).toBeTruthy()
+    expect(targets.length).toBeGreaterThan(1000)
+  })
+
+  // The user renamed it; that is the label they will look for.
+  it('prefers the company name over the BAS name on a collision', async () => {
+    const targets = await buildMappingTargets(
+      supabaseWith([
+        { account_number: '3001', account_name: 'Försäljning konsulttjänster', account_class: 3 },
+      ]),
+      'company-1',
+    )
+    const matches = targets.filter((t) => t.account_number === '3001')
+    expect(matches).toHaveLength(1)
+    expect(matches[0].account_name).toBe('Försäljning konsulttjänster')
+  })
+
+  it('derives the class from the number when the row has none', async () => {
+    const targets = await buildMappingTargets(
+      supabaseWith([{ account_number: '3005', account_name: 'X', account_class: null }]),
+      'company-1',
+    )
+    expect(targets.find((t) => t.account_number === '3005')?.account_class).toBe(3)
+  })
+
+  it('sorts by account number so the dropdown groups read in order', async () => {
+    const targets = await buildMappingTargets(
+      supabaseWith([{ account_number: '3005', account_name: 'X', account_class: 3 }]),
+      'company-1',
+    )
+    const numbers = targets.map((t) => t.account_number)
+    expect(numbers).toEqual([...numbers].sort((a, b) => a.localeCompare(b)))
+  })
+
+  // An incomplete list still lets the migration run; an exception stops it.
+  it('falls back to BAS when the chart cannot be read', async () => {
+    const targets = await buildMappingTargets(supabaseWith(new Error('boom')), 'company-1')
+    expect(targets.length).toBeGreaterThan(1000)
+    expect(targets.find((t) => t.account_number === '3005')).toBeUndefined()
+  })
+})
diff --git a/extensions/general/arcim-migration/index.ts b/extensions/general/arcim-migration/index.ts
index 184910c8..b76d0236 100644
--- a/extensions/general/arcim-migration/index.ts
+++ b/extensions/general/arcim-migration/index.ts
@@ -34,7 +34,7 @@ import { mergeParsedSIEFiles } from '@/lib/import/sie-merge'
 import { scanSieForCp1252Artifacts, formatSieArtifactWarning } from '@/lib/import/sie-artifact-scan'
 import { suggestMappings, getMappingStats, isSystemAccount } from '@/lib/import/account-mapper'
 import { loadMappings, generateImportPreview, executeSIEImport, findOverlappingPeriodImports } from '@/lib/import/sie-import'
-import { BAS_REFERENCE } from '@/lib/bookkeeping/bas-reference'
+import { buildMappingTargets } from './lib/mapping-targets'
 import type { ProviderName } from '@/lib/providers/types'
 import { FORTNOX_DOCUMENT_SCOPES_APPROVED } from '@/lib/providers/fortnox/oauth'
 import { errorResponseFromCode } from '@/lib/errors/get-structured-error'
@@ -1023,12 +1023,13 @@ export const arcimMigrationExtension: Extension = {
             updated_at: '',
           }))
 
-          // Suggest mappings
-          const basAccounts = BAS_REFERENCE.map(b => ({
-            account_number: b.account_number,
-            account_name: b.account_name,
-          }))
-          const mappings = suggestMappings(allAccounts, basAccounts, existingRecords)
+          // Mapping targets are the company's OWN chart of accounts first,
+          // then BAS for anything it does not have yet. BAS alone cannot
+          // express an account the company added outside the standard, so
+          // such an account was impossible to map onto. See
+          // ./lib/mapping-targets.
+          const mappingTargets = await buildMappingTargets(supabase, companyId)
+          const mappings = suggestMappings(allAccounts, mappingTargets, existingRecords)
           const mappingStats = getMappingStats(mappings)
 
           log.info(`Account mapping: ${allAccounts.length} unique accounts across ${sieFiles.length} files, ${mappingStats.unmapped} unmapped`)
@@ -1111,7 +1112,7 @@ export const arcimMigrationExtension: Extension = {
             // Allowed years whose provider export failed: the wizard warns
             // the user before proceeding so an IB/UB gap cannot slip through.
             failedYears,
-            basAccounts: BAS_REFERENCE,
+            basAccounts: mappingTargets,
           })
         } catch (error) {
           log.error('arcim sie-data fetch failed', error as Error)
diff --git a/extensions/general/arcim-migration/lib/mapping-targets.ts b/extensions/general/arcim-migration/lib/mapping-targets.ts
new file mode 100644
index 00000000..cbddcc2e
--- /dev/null
+++ b/extensions/general/arcim-migration/lib/mapping-targets.ts
@@ -0,0 +1,74 @@
+import type { SupabaseClient } from '@supabase/supabase-js'
+
+import { BAS_REFERENCE } from '@/lib/bookkeeping/bas-reference'
+import { fetchAllRows } from '@/lib/supabase/fetch-all'
+
+/** What the mapping step offers as a target, and what it renders per option. */
+export interface MappingTarget {
+  account_number: string
+  account_name: string
+  /** Grouping in the dropdown. Derived from the number when a row lacks it. */
+  account_class?: number
+}
+
+/** BAS numbers are 4 digits and the first is the class: 3005 is class 3. */
+function classOf(accountNumber: string): number | undefined {
+  const first = Number.parseInt(accountNumber.slice(0, 1), 10)
+  return Number.isFinite(first) ? first : undefined
+}
+
+/**
+ * The accounts a Fortnox source account may be mapped onto: the company's own
+ * chart first, then the BAS catalogue for standard accounts it has not created
+ * yet.
+ *
+ * Why both. BAS alone hides every account a company added outside the
+ * standard, and there are plenty: BAS defines 3000-3004 and stops, so an
+ * account like 3005 "Provisioner inom Sverige" can be active in the chart,
+ * listed everywhere else in the app, and still impossible to select as a
+ * mapping target. The company
+ * chart alone would be wrong in the other direction: on a first migration it
+ * can be nearly empty, and the user is mapping onto standard accounts the
+ * import is about to create.
+ *
+ * On a collision the company row wins. Its name is whatever the user renamed
+ * the account to, and that is the label they are looking for in the list.
+ *
+ * A failed read degrades to BAS rather than throwing: an incomplete list still
+ * lets the migration proceed, an error stops it dead.
+ */
+export async function buildMappingTargets(
+  supabase: SupabaseClient,
+  companyId: string,
+): Promise<MappingTarget[]> {
+  let own: MappingTarget[] = []
+  try {
+    const rows = await fetchAllRows(({ from, to }) =>
+      supabase
+        .from('chart_of_accounts')
+        .select('account_number, account_name, account_class')
+        .eq('company_id', companyId)
+        .order('account_number')
+        .range(from, to),
+    )
+    own = (rows as Array<Record<string, unknown>>).map((r) => ({
+      account_number: String(r.account_number),
+      account_name: String(r.account_name ?? ''),
+      account_class:
+        typeof r.account_class === 'number' ? r.account_class : classOf(String(r.account_number)),
+    }))
+  } catch {
+    own = []
+  }
+
+  const seen = new Set(own.map((a) => a.account_number))
+  const fromBas = BAS_REFERENCE.filter((b) => !seen.has(b.account_number)).map((b) => ({
+    account_number: b.account_number,
+    account_name: b.account_name,
+    account_class: classOf(b.account_number),
+  }))
+
+  // Sorted by number so the dropdown's per-class groups read in order
+  // regardless of which source a given account came from.
+  return [...own, ...fromBas].sort((a, b) => a.account_number.localeCompare(b.account_number))
+}