diff --git a/src/eligibility_signposting_api/services/calculators/eligibility_calculator.py b/src/eligibility_signposting_api/services/calculators/eligibility_calculator.py
index 0423e533..31419b83 100644
--- a/src/eligibility_signposting_api/services/calculators/eligibility_calculator.py
+++ b/src/eligibility_signposting_api/services/calculators/eligibility_calculator.py
@@ -13,6 +13,7 @@
 from eligibility_signposting_api.services.calculators.rule_calculator import RuleCalculator
 
 Row = Collection[Mapping[str, Any]]
+magic_cohort = "elid_all_people"
 
 
 @service
@@ -70,19 +71,22 @@ def get_the_base_eligible_campaigns(self, campaign_group: list[rules.CampaignCon
             return base_eligible_campaigns
         return []
 
-    def check_base_eligibility(self, iteration: rules.Iteration | None) -> set[str]:
+    def check_base_eligibility(self, iteration: rules.Iteration | None) -> bool:
         """Return cohorts for which person is base eligible."""
 
         if not iteration:
-            return set()
+            return False  # pragma: no cover
         iteration_cohorts: set[str] = {
             cohort.cohort_label for cohort in iteration.iteration_cohorts if cohort.cohort_label
         }
+        if magic_cohort in iteration_cohorts:
+            return True
+
         cohorts_row: Mapping[str, dict[str, dict[str, dict[str, Any]]]] = next(
             (row for row in self.person_data if row.get("ATTRIBUTE_TYPE") == "COHORTS"), {}
         )
         person_cohorts: set[str] = set(cohorts_row.get("COHORT_MAP", {}).get("cohorts", {}).get("M", {}).keys())
-        return iteration_cohorts & person_cohorts
+        return bool(iteration_cohorts & person_cohorts)
 
     def evaluate_eligibility_by_iteration_rules(
         self, campaign_group: list[rules.CampaignConfig]
diff --git a/tests/unit/services/calculators/test_eligibility_calculator.py b/tests/unit/services/calculators/test_eligibility_calculator.py
index 88c4c722..2e6ed793 100644
--- a/tests/unit/services/calculators/test_eligibility_calculator.py
+++ b/tests/unit/services/calculators/test_eligibility_calculator.py
@@ -46,6 +46,48 @@ def test_not_base_eligible(faker: Faker):
     )
 
 
+@pytest.mark.parametrize(
+    ("cohorts", "test_comment"),
+    [
+        (["elid_all_people"], "Only magic cohort present"),
+        (["elid_all_people", "cohort1"], "Magic cohort with other cohorts"),
+    ],
+)
+def test_base_eligible_with_when_magic_cohort_is_present(faker: Faker, cohorts, test_comment):
+    # Given
+    nhs_number = NHSNumber(faker.nhs_number())
+    date_of_birth = DateOfBirth(faker.date_of_birth(minimum_age=76, maximum_age=79))
+
+    person_rows = person_rows_builder(nhs_number, date_of_birth=date_of_birth, cohorts=["cohort1"])
+    campaign_configs = [
+        rule_builder.CampaignConfigFactory.build(
+            target="RSV",
+            iterations=[
+                rule_builder.IterationFactory.build(
+                    iteration_cohorts=[
+                        rule_builder.IterationCohortFactory.build(cohort_label=label) for label in cohorts
+                    ],
+                    iteration_rules=[rule_builder.PersonAgeSuppressionRuleFactory.build()],
+                )
+            ],
+        )
+    ]
+
+    calculator = EligibilityCalculator(person_rows, campaign_configs)
+
+    # When
+    actual = calculator.evaluate_eligibility()
+
+    # Then
+    assert_that(
+        actual,
+        is_eligibility_status().with_conditions(
+            has_item(is_condition().with_condition_name(ConditionName("RSV")).and_status(Status.actionable))
+        ),
+        test_comment,
+    )
+
+
 @freeze_time("2025-04-25")
 def test_only_live_campaigns_considered(faker: Faker):
     # Given