diff --git a/swh/model/model.py b/swh/model/model.py
--- a/swh/model/model.py
+++ b/swh/model/model.py
@@ -296,7 +296,8 @@
         return ov
 
     def unique_key(self) -> KeyType:
-        return {"origin": self.origin, "date": str(self.date)}
+        assert self.visit is not None
+        return {"origin": self.origin, "visit": str(self.visit)}
 
 
 @attr.s(frozen=True)
diff --git a/swh/model/tests/test_model.py b/swh/model/tests/test_model.py
--- a/swh/model/tests/test_model.py
+++ b/swh/model/tests/test_model.py
@@ -76,9 +76,9 @@
     date = datetime.datetime.now(tz=datetime.timezone.utc)
     id_ = b"42" * 10
     assert Origin(url=url).unique_key() == {"url": url}
-    assert OriginVisit(origin=url, date=date, type="git").unique_key() == {
+    assert OriginVisit(origin=url, visit=42, date=date, type="git").unique_key() == {
         "origin": url,
-        "date": str(date),
+        "visit": "42",
     }
     assert OriginVisitStatus(
         origin=url, visit=42, date=date, status="created", snapshot=None