diff --git a/CHANGELOG.md b/CHANGELOG.md
index 850650c36..89e7eaf08 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,11 +17,10 @@ General improvement for the Helm Chart:
 - add missing namespace label
 - make object name consistent
 
-### Changed
-
 - Upgrade `fastapi` to `0.100.0`
 - Upgrade `sentry_sdk` to `1.28.1`
 - Upgrade `uvicorn` to `0.23.0`
+- Enforce valid IRI for `activity` parameter in `GET /statements`
 
 ## [3.8.0] - 2023-06-21
 
diff --git a/src/ralph/api/routers/statements.py b/src/ralph/api/routers/statements.py
index c136a723b..f34988bde 100644
--- a/src/ralph/api/routers/statements.py
+++ b/src/ralph/api/routers/statements.py
@@ -30,6 +30,7 @@
     BaseXapiAgentWithMboxSha1Sum,
     BaseXapiAgentWithOpenId,
 )
+from ralph.models.xapi.base.common import IRI
 
 from ..models import ErrorDetail, LaxStatement
 
@@ -82,7 +83,7 @@ async def get(
         None,
         description="Filter, only return Statements matching the specified Verb id",
     ),
-    activity: Optional[str] = Query(
+    activity: Optional[IRI] = Query(
         None,
         description=(
             "Filter, only return Statements for which the Object "
@@ -231,7 +232,7 @@ async def get(
         raise HTTPException(
             status_code=status.HTTP_400_BAD_REQUEST,
             detail=(
-                "Querying by id only accepts `attachments` and `format` as extra"
+                "Querying by id only accepts `attachments` and `format` as extra "
                 "parameters"
             ),
         )
diff --git a/tests/api/test_statements_get.py b/tests/api/test_statements_get.py
index 28bad449e..c9c160e1e 100644
--- a/tests/api/test_statements_get.py
+++ b/tests/api/test_statements_get.py
@@ -67,6 +67,19 @@ def insert_clickhouse_statements(statements):
     assert success == len(statements)
 
 
+def create_mock_activity(id_: int = 0):
+    """Create distinct activites with valid IRIs.
+
+    args:
+        id_: An integer used to uniquely identify the created agent.
+
+    """
+    return {
+        "objectType": "Activity",
+        "id": f"http://example.com/activity_{id_}",
+    }
+
+
 def create_mock_agent(ifi: str, id_: int, home_page_id=None):
     """Create distinct mock agents with a given Inverse Functional Identifier.
 
@@ -310,34 +323,40 @@ def test_api_statements_get_statements_by_activity(
     """
     # pylint: disable=redefined-outer-name
 
+    activity_0 = create_mock_activity(0)
+    activity_1 = create_mock_activity(1)
+
     statements = [
         {
             "id": "be67b160-d958-4f51-b8b8-1892002dbac6",
             "timestamp": datetime.now().isoformat(),
-            "object": {
-                "id": "58d8bede-155f-48b1-b1ff-a41eb28c2f0b",
-                "objectType": "Activity",
-            },
+            "object": activity_0,
         },
         {
             "id": "72c81e98-1763-4730-8cfc-f5ab34f1bad2",
             "timestamp": datetime.now().isoformat(),
-            "object": {
-                "id": "a2956991-200b-40a7-9548-293cdcc06c4b",
-                "objectType": "Activity",
-            },
+            "object": activity_1,
         },
     ]
     insert_statements_and_monkeypatch_backend(statements)
 
     response = client.get(
-        "/xAPI/statements/?activity=a2956991-200b-40a7-9548-293cdcc06c4b",
+        f"/xAPI/statements/?activity={activity_1['id']}",
         headers={"Authorization": f"Basic {auth_credentials}"},
     )
 
     assert response.status_code == 200
     assert response.json() == {"statements": [statements[1]]}
 
+    # Check that badly formated activity returns an error
+    response = client.get(
+        "/xAPI/statements/?activity=INVALID_IRI",
+        headers={"Authorization": f"Basic {auth_credentials}"},
+    )
+
+    assert response.status_code == 422
+    assert response.json()["detail"][0]["msg"] == "'INVALID_IRI' is not a valid 'IRI'."
+
 
 def test_api_statements_get_statements_since_timestamp(
     insert_statements_and_monkeypatch_backend, auth_credentials
@@ -606,7 +625,7 @@ def test_api_statements_get_statements_invalid_query_parameters(
 
     # Check for error when invalid parameters are provided with a statementId
     for invalid_param, value in [
-        ("activity", "activity_1"),
+        ("activity", create_mock_activity()["id"]),
         ("agent", json.dumps(create_mock_agent("mbox", 1))),
         ("verb", "verb_1"),
     ]:
@@ -615,6 +634,12 @@ def test_api_statements_get_statements_invalid_query_parameters(
             headers={"Authorization": f"Basic {auth_credentials}"},
         )
         assert response.status_code == 400
+        assert response.json() == {
+            "detail": (
+                "Querying by id only accepts `attachments` and `format` as "
+                "extra parameters"
+            )
+        }
 
     # Check for NO 400 when statementId is passed with authorized parameters
     for valid_param, value in [("format", "ids"), ("attachments", "true")]: