diff --git a/requirements-swh.txt b/requirements-swh.txt
--- a/requirements-swh.txt
+++ b/requirements-swh.txt
@@ -1,4 +1,4 @@
 swh.core >= 0.0.75
-swh.model >= 0.0.60
+swh.model >= 0.3.0
 swh.scheduler
 swh.storage >= 0.0.189
diff --git a/swh/loader/package/archive/loader.py b/swh/loader/package/archive/loader.py
--- a/swh/loader/package/archive/loader.py
+++ b/swh/loader/package/archive/loader.py
@@ -129,7 +129,7 @@
             author=SWH_PERSON,
             committer=SWH_PERSON,
             committer_date=normalized_time,
-            parents=[],
+            parents=(),
             directory=directory,
             synthetic=True,
             metadata={
diff --git a/swh/loader/package/cran/loader.py b/swh/loader/package/cran/loader.py
--- a/swh/loader/package/cran/loader.py
+++ b/swh/loader/package/cran/loader.py
@@ -104,7 +104,7 @@
             author=author,
             committer=author,
             committer_date=date,
-            parents=[],
+            parents=(),
             directory=directory,
             synthetic=True,
             metadata={
diff --git a/swh/loader/package/debian/loader.py b/swh/loader/package/debian/loader.py
--- a/swh/loader/package/debian/loader.py
+++ b/swh/loader/package/debian/loader.py
@@ -153,7 +153,7 @@
             date=date,
             committer=author,
             committer_date=date,
-            parents=[],
+            parents=(),
             directory=directory,
             synthetic=True,
             metadata={
diff --git a/swh/loader/package/deposit/loader.py b/swh/loader/package/deposit/loader.py
--- a/swh/loader/package/deposit/loader.py
+++ b/swh/loader/package/deposit/loader.py
@@ -97,7 +97,7 @@
             date=date,
             committer=committer,
             committer_date=commit_date,
-            parents=[hash_to_bytes(p) for p in depo["revision_parents"]],
+            parents=tuple([hash_to_bytes(p) for p in depo["revision_parents"]]),
             directory=directory,
             synthetic=True,
             metadata={
diff --git a/swh/loader/package/nixguix/loader.py b/swh/loader/package/nixguix/loader.py
--- a/swh/loader/package/nixguix/loader.py
+++ b/swh/loader/package/nixguix/loader.py
@@ -153,7 +153,7 @@
             date=None,
             committer=EMPTY_AUTHOR,
             committer_date=None,
-            parents=[],
+            parents=(),
             directory=directory,
             synthetic=True,
             metadata={
diff --git a/swh/loader/package/npm/loader.py b/swh/loader/package/npm/loader.py
--- a/swh/loader/package/npm/loader.py
+++ b/swh/loader/package/npm/loader.py
@@ -121,7 +121,7 @@
             date=date,
             committer=author,
             committer_date=date,
-            parents=[],
+            parents=(),
             directory=directory,
             synthetic=True,
             metadata={
diff --git a/swh/loader/package/pypi/loader.py b/swh/loader/package/pypi/loader.py
--- a/swh/loader/package/pypi/loader.py
+++ b/swh/loader/package/pypi/loader.py
@@ -101,7 +101,7 @@
             date=date,
             committer=_author,
             committer_date=date,
-            parents=[],
+            parents=(),
             directory=directory,
             synthetic=True,
             metadata={