diff --git a/api/src/schemas/statements.py b/api/src/schemas/statements.py
index e2d0a56..c546d2a 100644
--- a/api/src/schemas/statements.py
+++ b/api/src/schemas/statements.py
@@ -9,8 +9,9 @@ import datetime
 import uuid
 from collections.abc import Sequence
 from decimal import Decimal
+from typing import Annotated
 
-from pydantic import BaseModel, ConfigDict, Field
+from pydantic import BaseModel, ConfigDict, Field, StringConstraints
 
 from src.domain.statement_checks import ChecksReport, FailedCheck
 from src.models.enums import DocumentCheckResult, DocumentStatus, DocumentType, PeriodQuarter
@@ -237,13 +238,16 @@ class CellPatch(BaseModel):
 
 
 class HeaderPatch(BaseModel):
-    """Отсутствующее поле не меняется; `null` у `report_date`/`inn` — очистить значение (`model_fields_set`)."""
+    """Отсутствующее поле не меняется; `null` у `report_date`/`inn` — очистить значение (`model_fields_set`).
+
+    `units: null` — «не менять» (единицы измерения очищать нельзя); непустая строка после обрезки пробелов, до 50
+    символов (пробельная строка — 422)."""
 
     model_config = ConfigDict(extra="forbid")
 
     inn: str | None = None
     report_date: datetime.date | None = None
-    units: str | None = Field(None, min_length=1, max_length=50)
+    units: Annotated[str, StringConstraints(strip_whitespace=True, min_length=1, max_length=50)] | None = None
 
 
 class StatementPatch(BaseModel):
diff --git a/api/src/services/statements.py b/api/src/services/statements.py
index 37c59c3..9812950 100644
--- a/api/src/services/statements.py
+++ b/api/src/services/statements.py
@@ -202,7 +202,11 @@ class StatementService:
         if not after:
             return await self.build_out(document, meta)
         if meta.checks_accepted_at is not None:
-            before["checks_accepted"] = {"by": meta.checks_accepted_by, "at": meta.checks_accepted_at}
+            before["checks_accepted"] = {
+                "by": meta.checks_accepted_by,
+                "at": meta.checks_accepted_at,
+                "comment": meta.checks_accepted_comment,
+            }
             after["checks_accepted"] = None
             meta.checks_accepted_by = meta.checks_accepted_at = meta.checks_accepted_comment = None
         await self._session.flush()
diff --git a/api/tests/test_api_statements.py b/api/tests/test_api_statements.py
index 5a6d69e..1d9ba08 100644
--- a/api/tests/test_api_statements.py
+++ b/api/tests/test_api_statements.py
@@ -410,6 +410,7 @@ async def test_patch_rereads_meta_under_lock(
     assert held.checks_accepted_at is None and held.checks_accepted_comment is None
     event = (await seeded.execute(select(AuditEvent).where(AuditEvent.object_id == document.id))).scalars().one()
     assert event.before_value["checks_accepted"]["by"] == str(user_id) and event.after_value["checks_accepted"] is None
+    assert event.before_value["checks_accepted"]["comment"] == "x"  # T6.4: сброшенный комментарий акцепта сохранён
 
 
 async def test_patch_duplicate_cell_rejected(
@@ -713,3 +714,27 @@ async def test_confirmed_form_in_checklist(
         )
     ).scalar_one()
     assert meta.reviewed_by == user.id
+
+
+@pytest.mark.parametrize("units", ["   ", "", "я" * 51])
+async def test_patch_units_invalid_is_422(
+    seeded: AsyncSession, fixtures_dir: Path, auth_client: AuthClientFactory, units: str
+) -> None:
+    """T6.2: пробельная, пустая и длиннее 50 символов единицы измерения отклоняются; `null` — «не менять»."""
+    document = await form(seeded, fixtures_dir)
+    client = await auth_client(KA_RF)
+    url = f"/documents/{document.id}/statement"
+    response = await client.patch(url, json={"header": {"units": units}})
+    assert response.status_code == HTTPStatus.UNPROCESSABLE_ENTITY, response.text
+    unchanged = await client.patch(url, json={"header": {"units": None}})
+    assert unchanged.status_code == HTTPStatus.OK
+
+
+async def test_patch_units_are_stripped(
+    seeded: AsyncSession, fixtures_dir: Path, auth_client: AuthClientFactory
+) -> None:
+    document = await form(seeded, fixtures_dir)
+    client = await auth_client(KA_RF)
+    response = await client.patch(f"/documents/{document.id}/statement", json={"header": {"units": "  тыс. руб.  "}})
+    assert response.status_code == HTTPStatus.OK, response.text
+    assert response.json()["header"]["units"]["value"] == "тыс. руб."