diff --git a/backend/ee/authentication/scim/utils.py b/backend/ee/authentication/scim/utils.py
index 9119973a0..ea7ef001a 100644
--- a/backend/ee/authentication/scim/utils.py
+++ b/backend/ee/authentication/scim/utils.py
@@ -16,9 +16,11 @@
     role_has_managed_key,
 )
 from api.utils.keys import revoke_team_environment_keys
+from ee.authentication.scim.constants import SCIM_DEFAULT_COUNT
 from ee.authentication.scim.exceptions import (
     SCIMDeactivationForbidden,
     SCIMProvisioningConflict,
+    scim_bad_request,
 )
 
 logger = logging.getLogger(__name__)
@@ -199,3 +201,29 @@ def reactivate_scim_user(scim_user):
     if scim_user.org_member and scim_user.org_member.deleted_at is not None:
         scim_user.org_member.deleted_at = None
         scim_user.org_member.save(update_fields=["deleted_at"])
+
+
+def parse_pagination_params(request):
+    """Parse the SCIM startIndex and count query parameters.
+
+    Returns (start_index, count, None) on success, or (None, None, response)
+    where response is a SCIM 400. Both parameters are client supplied, so a
+    non-integer must be reported rather than raised. Per RFC 7644 section 3.4.2.4
+    startIndex is 1-based and a negative count is interpreted as zero, which also
+    keeps the value out of a negative queryset slice.
+    """
+    raw_start = request.GET.get("startIndex", 1)
+    try:
+        start_index = max(int(raw_start), 1)
+    except (TypeError, ValueError):
+        return None, None, scim_bad_request(
+            f"startIndex must be an integer, got {raw_start!r}"
+        )
+
+    raw_count = request.GET.get("count", SCIM_DEFAULT_COUNT)
+    try:
+        count = min(int(raw_count), SCIM_DEFAULT_COUNT)
+    except (TypeError, ValueError):
+        return None, None, scim_bad_request(f"count must be an integer, got {raw_count!r}")
+
+    return start_index, max(count, 0), None
diff --git a/backend/ee/authentication/scim/views/groups.py b/backend/ee/authentication/scim/views/groups.py
index 66f1de1be..ffd0d000b 100644
--- a/backend/ee/authentication/scim/views/groups.py
+++ b/backend/ee/authentication/scim/views/groups.py
@@ -27,8 +27,7 @@
 )
 from api.utils.keys import provision_team_environment_keys, revoke_team_environment_keys
 from ee.authentication.scim.auth import SCIMTokenAuthentication
-from ee.authentication.scim.constants import SCIM_DEFAULT_COUNT
-from ee.authentication.scim.utils import resolve_external_id
+from ee.authentication.scim.utils import parse_pagination_params, resolve_external_id
 from ee.authentication.scim.exceptions import (
     scim_bad_request,
     scim_conflict,
@@ -232,8 +231,9 @@ def groups_detail(request, scim_group_id):
 
 def _list_groups(request, org):
     filter_str = request.GET.get("filter", "")
-    start_index = max(int(request.GET.get("startIndex", 1)), 1)
-    count = min(int(request.GET.get("count", SCIM_DEFAULT_COUNT)), SCIM_DEFAULT_COUNT)
+    start_index, count, error = parse_pagination_params(request)
+    if error:
+        return error
 
     qs = SCIMGroup.objects.filter(organisation=org).order_by("created_at")
     if filter_str:
diff --git a/backend/ee/authentication/scim/views/users.py b/backend/ee/authentication/scim/views/users.py
index 28156c874..b69459684 100644
--- a/backend/ee/authentication/scim/views/users.py
+++ b/backend/ee/authentication/scim/views/users.py
@@ -38,13 +38,13 @@
     SCIM_USER_ATTR_MAP,
     scim_filter_to_queryset,
 )
-from ee.authentication.scim.constants import SCIM_DEFAULT_COUNT
 from ee.authentication.scim.serializers import (
     serialize_list_response,
     serialize_scim_user,
 )
 from ee.authentication.scim.logging import log_scim_event
 from ee.authentication.scim.utils import (
+    parse_pagination_params,
     deactivate_scim_user,
     provision_scim_user,
     reactivate_scim_user,
@@ -135,8 +135,9 @@ def users_detail(request, scim_user_id):
 
 def _list_users(request, org):
     filter_str = request.GET.get("filter", "")
-    start_index = max(int(request.GET.get("startIndex", 1)), 1)
-    count = min(int(request.GET.get("count", SCIM_DEFAULT_COUNT)), SCIM_DEFAULT_COUNT)
+    start_index, count, error = parse_pagination_params(request)
+    if error:
+        return error
 
     qs = SCIMUser.objects.filter(organisation=org).order_by("created_at")
     if filter_str:
diff --git a/backend/tests/ee/authentication/scim/test_pagination_params.py b/backend/tests/ee/authentication/scim/test_pagination_params.py
new file mode 100644
index 000000000..f880a4805
--- /dev/null
+++ b/backend/tests/ee/authentication/scim/test_pagination_params.py
@@ -0,0 +1,68 @@
+"""Tests for SCIM startIndex/count parsing on the list endpoints.
+
+startIndex and count come straight from the client, so a malformed value has to
+come back as a SCIM 400 rather than a 500.
+"""
+
+from unittest.mock import MagicMock
+
+import pytest
+
+from ee.authentication.scim.constants import SCIM_DEFAULT_COUNT
+from ee.authentication.scim.utils import parse_pagination_params
+
+
+def _request(**params):
+    request = MagicMock()
+    request.GET = params
+    return request
+
+
+def test_defaults_when_absent():
+    start_index, count, error = parse_pagination_params(_request())
+    assert error is None
+    assert start_index == 1
+    assert count == SCIM_DEFAULT_COUNT
+
+
+def test_valid_values_are_used():
+    start_index, count, error = parse_pagination_params(
+        _request(startIndex="5", count="20")
+    )
+    assert error is None
+    assert (start_index, count) == (5, 20)
+
+
+@pytest.mark.parametrize("bad", ["abc", "", "1.5", "null", "1,000"])
+def test_non_integer_start_index_is_a_400(bad):
+    start_index, count, error = parse_pagination_params(_request(startIndex=bad))
+    assert (start_index, count) == (None, None)
+    assert error.status_code == 400
+
+
+@pytest.mark.parametrize("bad", ["abc", "", "1.5"])
+def test_non_integer_count_is_a_400(bad):
+    start_index, count, error = parse_pagination_params(_request(count=bad))
+    assert (start_index, count) == (None, None)
+    assert error.status_code == 400
+
+
+def test_start_index_is_clamped_to_one():
+    # RFC 7644 3.4.2.4: a value less than 1 is interpreted as 1.
+    start_index, _, error = parse_pagination_params(_request(startIndex="-3"))
+    assert error is None
+    assert start_index == 1
+
+
+def test_negative_count_becomes_zero():
+    # Left negative this would reach the queryset as qs[0:-5], and Django raises
+    # ValueError("Negative indexing is not supported.").
+    _, count, error = parse_pagination_params(_request(count="-5"))
+    assert error is None
+    assert count == 0
+
+
+def test_count_is_capped_at_the_default():
+    _, count, error = parse_pagination_params(_request(count="100000"))
+    assert error is None
+    assert count == SCIM_DEFAULT_COUNT