diff --git a/swh/deposit/api/common.py b/swh/deposit/api/common.py
--- a/swh/deposit/api/common.py
+++ b/swh/deposit/api/common.py
@@ -104,6 +104,25 @@
     return h.digest()
 
 
+def get_deposit_by_id(
+    deposit_id: int, collection_name: Optional[str] = None
+) -> Deposit:
+    """Gets an existing Deposit object if it exists, or raises `DepositError`.
+    If `collection` is not None, also checks the deposit belongs to the collection."""
+    try:
+        deposit = Deposit.objects.get(pk=deposit_id)
+    except Deposit.DoesNotExist:
+        raise DepositError(NOT_FOUND, f"Deposit {deposit_id} does not exist")
+
+    if collection_name and deposit.collection.name != collection_name:
+        raise DepositError(
+            NOT_FOUND,
+            f"Deposit {deposit_id} does not belong to collection {collection_name}",
+        )
+
+    return deposit
+
+
 class AuthenticatedAPIView(APIView):
     """Mixin intended as a based API view to enforce the basic
        authentication check
@@ -217,7 +236,7 @@
                 parent=deposit_parent,
             )
         else:
-            deposit = Deposit.objects.get(pk=deposit_id)
+            deposit = get_deposit_by_id(deposit_id)
 
             # update metadata
             deposit.complete_date = complete_date
@@ -295,10 +314,7 @@
         """Delete archive references from the deposit id.
 
         """
-        try:
-            deposit = Deposit.objects.get(pk=deposit_id)
-        except Deposit.DoesNotExist:
-            raise DepositError(NOT_FOUND, f"The deposit {deposit_id} does not exist")
+        deposit = get_deposit_by_id(deposit_id)
         DepositRequest.objects.filter(deposit=deposit, type=ARCHIVE_TYPE).delete()
 
         return {}
@@ -315,10 +331,7 @@
             Dict with error key to describe the failure.
 
         """
-        try:
-            deposit = Deposit.objects.get(pk=deposit_id)
-        except Deposit.DoesNotExist:
-            raise DepositError(NOT_FOUND, f"The deposit {deposit_id} does not exist")
+        deposit = get_deposit_by_id(deposit_id)
 
         if deposit.collection.name != collection_name:
             summary = "Cannot delete a deposit from another collection"
@@ -821,7 +834,7 @@
             collection_name: the associated client
             deposit_id: deposit identifier
         """
-        deposit = Deposit.objects.get(pk=deposit_id)
+        deposit = get_deposit_by_id(deposit_id)
         deposit.complete_date = timezone.now()
         deposit.status = DEPOSIT_STATUS_DEPOSITED
         deposit.save()
@@ -878,12 +891,7 @@
         headers = self._read_headers(request)
 
         if deposit_id:
-            try:
-                deposit = Deposit.objects.get(pk=deposit_id)
-            except Deposit.DoesNotExist:
-                raise DepositError(
-                    NOT_FOUND, f"Deposit with id {deposit_id} does not exist"
-                )
+            deposit = get_deposit_by_id(deposit_id)
 
             assert deposit is not None
             self.restrict_access(request, headers, deposit)
diff --git a/swh/deposit/api/content.py b/swh/deposit/api/content.py
--- a/swh/deposit/api/content.py
+++ b/swh/deposit/api/content.py
@@ -7,9 +7,8 @@
 from django.shortcuts import render
 from rest_framework import status
 
-from ..errors import NOT_FOUND, make_error_response
-from ..models import DEPOSIT_STATUS_DETAIL, Deposit, DepositRequest
-from .common import APIBase
+from ..models import DEPOSIT_STATUS_DETAIL, DepositRequest
+from .common import APIBase, get_deposit_by_id
 
 
 class ContentAPI(APIBase):
@@ -24,17 +23,7 @@
     def get(self, req, collection_name: str, deposit_id: int) -> HttpResponse:
         self.checks(req, collection_name, deposit_id)
 
-        try:
-            deposit = Deposit.objects.get(pk=deposit_id)
-            if deposit.collection.name != collection_name:
-                raise Deposit.DoesNotExist
-        except Deposit.DoesNotExist:
-            return make_error_response(
-                req,
-                NOT_FOUND,
-                "deposit %s does not belong to collection %s"
-                % (deposit_id, collection_name),
-            )
+        deposit = get_deposit_by_id(deposit_id, collection_name)
 
         requests = DepositRequest.objects.filter(deposit=deposit)
         context = {
diff --git a/swh/deposit/api/edit.py b/swh/deposit/api/edit.py
--- a/swh/deposit/api/edit.py
+++ b/swh/deposit/api/edit.py
@@ -11,7 +11,7 @@
 from ..config import DEPOSIT_STATUS_LOAD_SUCCESS
 from ..errors import BAD_REQUEST, DepositError, ParserError
 from ..parsers import SWHAtomEntryParser, SWHMultiPartParser
-from .common import APIDelete, APIPut, ParsedRequestHeaders
+from .common import APIDelete, APIPut, ParsedRequestHeaders, get_deposit_by_id
 
 
 class EditAPI(APIPut, APIDelete):
@@ -97,7 +97,7 @@
         # Write to the metadata storage (and the deposit backend)
         # no ingestion triggered
 
-        deposit = Deposit.objects.get(pk=deposit_id)
+        deposit = get_deposit_by_id(deposit_id, collection_name)
         assert deposit.status == DEPOSIT_STATUS_LOAD_SUCCESS
 
         if swhid != deposit.swhid:
diff --git a/swh/deposit/api/private/__init__.py b/swh/deposit/api/private/__init__.py
--- a/swh/deposit/api/private/__init__.py
+++ b/swh/deposit/api/private/__init__.py
@@ -9,10 +9,10 @@
 
 from swh.deposit import utils
 from swh.deposit.api.common import AuthenticatedAPIView
-from swh.deposit.errors import NOT_FOUND, DepositError
 
 from ...config import METADATA_TYPE, APIConfig
 from ...models import Deposit, DepositRequest
+from ..common import get_deposit_by_id
 
 
 class DepositReadMixin:
@@ -32,7 +32,7 @@
 
         """
         if isinstance(deposit, int):
-            deposit = Deposit.objects.get(pk=deposit)
+            deposit = get_deposit_by_id(deposit)
 
         deposit_requests = DepositRequest.objects.filter(
             type=request_type, deposit=deposit
@@ -78,12 +78,7 @@
 
         """
         if deposit_id:
-            try:
-                Deposit.objects.get(pk=deposit_id)
-            except Deposit.DoesNotExist:
-                raise DepositError(
-                    NOT_FOUND, "Deposit with id %s does not exist" % deposit_id
-                )
+            get_deposit_by_id(deposit_id)
 
         headers = self._read_headers(req)
         self.additional_checks(req, headers, collection_name, deposit_id)
diff --git a/swh/deposit/api/private/deposit_check.py b/swh/deposit/api/private/deposit_check.py
--- a/swh/deposit/api/private/deposit_check.py
+++ b/swh/deposit/api/private/deposit_check.py
@@ -19,7 +19,7 @@
 from ...config import ARCHIVE_TYPE, DEPOSIT_STATUS_REJECTED, DEPOSIT_STATUS_VERIFIED
 from ...models import Deposit, DepositRequest
 from ..checks import check_metadata
-from ..common import APIGet
+from ..common import APIGet, get_deposit_by_id
 
 MANDATORY_ARCHIVE_UNREADABLE = (
     "At least one of its associated archives is not readable"  # noqa
@@ -145,7 +145,7 @@
             Tuple status, stream of content, content-type
 
         """
-        deposit = Deposit.objects.get(pk=deposit_id)
+        deposit = get_deposit_by_id(deposit_id)
         metadata, _ = self._metadata_get(deposit)
         problems: Dict = {}
         # will check each deposit's associated request (both of type
diff --git a/swh/deposit/api/private/deposit_read.py b/swh/deposit/api/private/deposit_read.py
--- a/swh/deposit/api/private/deposit_read.py
+++ b/swh/deposit/api/private/deposit_read.py
@@ -19,7 +19,7 @@
 from . import APIPrivateView, DepositReadMixin
 from ...config import ARCHIVE_TYPE, SWH_PERSON
 from ...models import Deposit
-from ..common import APIGet
+from ..common import APIGet, get_deposit_by_id
 
 
 @contextmanager
@@ -195,6 +195,6 @@
     def process_get(
         self, request, collection_name: str, deposit_id: int
     ) -> Tuple[int, Dict, str]:
-        deposit = Deposit.objects.get(pk=deposit_id)
+        deposit = get_deposit_by_id(deposit_id)
         data = self.metadata_read(deposit)
         return status.HTTP_200_OK, data if data else {}, "application/json"
diff --git a/swh/deposit/api/private/deposit_update_status.py b/swh/deposit/api/private/deposit_update_status.py
--- a/swh/deposit/api/private/deposit_update_status.py
+++ b/swh/deposit/api/private/deposit_update_status.py
@@ -9,8 +9,8 @@
 
 from . import APIPrivateView
 from ...errors import BAD_REQUEST, DepositError
-from ...models import DEPOSIT_STATUS_DETAIL, DEPOSIT_STATUS_LOAD_SUCCESS, Deposit
-from ..common import APIPut, ParsedRequestHeaders
+from ...models import DEPOSIT_STATUS_DETAIL, DEPOSIT_STATUS_LOAD_SUCCESS
+from ..common import APIPut, ParsedRequestHeaders, get_deposit_by_id
 
 MANDATORY_KEYS = ["origin_url", "revision_id", "directory_id", "snapshot_id"]
 
@@ -79,7 +79,7 @@
         """
         data = request.data
 
-        deposit = Deposit.objects.get(pk=deposit_id)
+        deposit = get_deposit_by_id(deposit_id)
 
         status = data["status"]
         deposit.status = status
diff --git a/swh/deposit/api/state.py b/swh/deposit/api/state.py
--- a/swh/deposit/api/state.py
+++ b/swh/deposit/api/state.py
@@ -7,9 +7,8 @@
 from django.shortcuts import render
 from rest_framework import status
 
-from ..errors import NOT_FOUND, make_error_response
-from ..models import DEPOSIT_STATUS_DETAIL, Deposit
-from .common import APIBase
+from ..models import DEPOSIT_STATUS_DETAIL
+from .common import APIBase, get_deposit_by_id
 from .converters import convert_status_detail
 
 
@@ -25,17 +24,7 @@
     def get(self, req, collection_name: str, deposit_id: int) -> HttpResponse:
         self.checks(req, collection_name, deposit_id)
 
-        try:
-            deposit = Deposit.objects.get(pk=deposit_id)
-            if deposit.collection.name != collection_name:
-                raise Deposit.DoesNotExist
-        except Deposit.DoesNotExist:
-            return make_error_response(
-                req,
-                NOT_FOUND,
-                "deposit %s does not belong to collection %s"
-                % (deposit_id, collection_name),
-            )
+        deposit = get_deposit_by_id(deposit_id, collection_name)
 
         status_detail = convert_status_detail(deposit.status_detail)
         if not status_detail:
diff --git a/swh/deposit/tests/api/test_deposit_private_read_metadata.py b/swh/deposit/tests/api/test_deposit_private_read_metadata.py
--- a/swh/deposit/tests/api/test_deposit_private_read_metadata.py
+++ b/swh/deposit/tests/api/test_deposit_private_read_metadata.py
@@ -394,5 +394,5 @@
     for url in private_get_raw_url_endpoints(deposit_collection, unknown_id):
         response = authenticated_client.get(url)
         assert response.status_code == status.HTTP_404_NOT_FOUND
-        msg = "Deposit with id %s does not exist" % unknown_id
+        msg = "Deposit %s does not exist" % unknown_id
         assert msg in response.content.decode("utf-8")
diff --git a/swh/deposit/tests/api/test_deposit_update.py b/swh/deposit/tests/api/test_deposit_update.py
--- a/swh/deposit/tests/api/test_deposit_update.py
+++ b/swh/deposit/tests/api/test_deposit_update.py
@@ -409,7 +409,7 @@
     assert response.status_code == status.HTTP_404_NOT_FOUND
     response_content = parse_xml(response.content)
     assert (
-        "Deposit with id %s does not exist" % unknown_deposit_id
+        "Deposit %s does not exist" % unknown_deposit_id
         == response_content["sword:error"]["summary"]
     )
 
@@ -433,7 +433,7 @@
     assert response.status_code == status.HTTP_404_NOT_FOUND
     response_content = parse_xml(response.content)
     assert (
-        "Deposit with id %s does not exist" % unknown_deposit_id
+        "Deposit %s does not exist" % unknown_deposit_id
         == response_content["sword:error"]["summary"]
     )
 
@@ -457,7 +457,7 @@
     assert response.status_code == status.HTTP_404_NOT_FOUND
     response_content = parse_xml(response.content)
     assert (
-        "Deposit with id %s does not exist" % unknown_deposit_id
+        "Deposit %s does not exist" % unknown_deposit_id
         == response_content["sword:error"]["summary"]
     )