diff --git a/changelog_entry.yaml b/changelog_entry.yaml
index e69de29b..4d118c82 100644
--- a/changelog_entry.yaml
+++ b/changelog_entry.yaml
@@ -0,0 +1,6 @@
+- bump: minor
+  changes:
+    changed:
+    - Shallow copy GroupEntities and PopulationEntity when cloning TaxBenefitSystem object
+    added:
+    - Two tests related to extensions that were previously removed
\ No newline at end of file
diff --git a/policyengine_core/taxbenefitsystems/tax_benefit_system.py b/policyengine_core/taxbenefitsystems/tax_benefit_system.py
index 98f812f1..d65dd1bb 100644
--- a/policyengine_core/taxbenefitsystems/tax_benefit_system.py
+++ b/policyengine_core/taxbenefitsystems/tax_benefit_system.py
@@ -667,6 +667,8 @@ def clone(self) -> "TaxBenefitSystem":
                 "_parameters_at_instant_cache",
                 "variables",
                 "entities",
+                "person_entity",
+                "group_entities",
             ):
                 new_dict[key] = value
 
@@ -676,10 +678,21 @@ def clone(self) -> "TaxBenefitSystem":
             variable_name: variable.clone()
             for variable_name, variable in self.variables.items()
         }
+
+        # Apply shallow copies to all relevant entities
         new_dict["entities"] = [copy.copy(entity) for entity in self.entities]
+        new_dict["person_entity"] = copy.copy(self.person_entity)
+        new_dict["group_entities"] = [
+            copy.copy(entity) for entity in self.group_entities
+        ]
 
+        # For all shallow-copied entities, set entity._tax_benefit_system to the new system
         for entity in new_dict["entities"]:
             entity.set_tax_benefit_system(new)
+        for entity in new_dict["group_entities"]:
+            entity.set_tax_benefit_system(new)
+        new_dict["person_entity"].set_tax_benefit_system(new)
+
         return new
 
     def entities_plural(self) -> dict:
diff --git a/tests/core/test_yaml.py b/tests/core/test_yaml.py
index 24ad6f3c..acb740d1 100644
--- a/tests/core/test_yaml.py
+++ b/tests/core/test_yaml.py
@@ -76,6 +76,13 @@ def test_with_reform(tax_benefit_system):
     )
 
 
+def test_with_extension(tax_benefit_system):
+    assert (
+        run_yaml_test(tax_benefit_system, "test_with_extension.yaml")
+        == EXIT_OK
+    )
+
+
 def test_with_anchors(tax_benefit_system):
     assert (
         run_yaml_test(tax_benefit_system, "test_with_anchors.yaml") == EXIT_OK
diff --git a/tests/fixtures/yaml_tests/test_with_extension.yaml b/tests/fixtures/yaml_tests/test_with_extension.yaml
new file mode 100644
index 00000000..682e512f
--- /dev/null
+++ b/tests/fixtures/yaml_tests/test_with_extension.yaml
@@ -0,0 +1,28 @@
+- name: "Test using an extension"
+  period: 2017-01
+  extensions:
+    - policyengine_core.extension_template
+  input:
+    persons:
+      parent: {}
+      child1: {}
+    household:
+      parents: [parent]
+      children: [child1]
+  output:
+    local_town_child_allowance: 100
+
+- name: "Test using an extension"
+  period: 2017-01
+  extensions:
+    - policyengine_core.extension_template
+  input:
+    persons:
+      parent: {}
+      child1: {}
+      child2: {}
+    household:
+      parents: [parent]
+      children: [child1, child2]
+  output:
+    local_town_child_allowance: 200
\ No newline at end of file