diff --git a/swh/model/collections.py b/swh/model/collections.py
index 2724f85..495b43c 100644
--- a/swh/model/collections.py
+++ b/swh/model/collections.py
@@ -1,49 +1,56 @@
 # Copyright (C) 2020 The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 from collections.abc import Mapping
 from typing import Dict, Generic, Iterable, Optional, Tuple, TypeVar, Union
 
 KT = TypeVar("KT")
 VT = TypeVar("VT")
 
 
 class ImmutableDict(Mapping, Generic[KT, VT]):
     data: Tuple[Tuple[KT, VT], ...]
 
-    def __init__(self, data: Union[Iterable[Tuple[KT, VT]], Dict[KT, VT]] = {}):
+    def __init__(
+        self,
+        data: Union[
+            Iterable[Tuple[KT, VT]], "ImmutableDict[KT, VT]", Dict[KT, VT]
+        ] = {},
+    ):
         if isinstance(data, dict):
             self.data = tuple(item for item in data.items())
+        elif isinstance(data, ImmutableDict):
+            self.data = data.data
         else:
             self.data = tuple(data)
 
     def __getitem__(self, key):
         for (k, v) in self.data:
             if k == key:
                 return v
         raise KeyError(key)
 
     def __iter__(self):
         for (k, v) in self.data:
             yield k
 
     def __len__(self):
         return len(self.data)
 
     def items(self):
         yield from self.data
 
     def copy_pop(self, popped_key) -> Tuple[Optional[VT], "ImmutableDict[KT, VT]"]:
         """Returns a copy of this ImmutableDict without the given key,
         as well as the value associated to the key."""
         popped_value = None
         new_items = []
         for (key, value) in self.data:
             if key == popped_key:
                 popped_value = value
             else:
                 new_items.append((key, value))
 
         return (popped_value, ImmutableDict(new_items))
diff --git a/swh/model/tests/test_collections.py b/swh/model/tests/test_collections.py
index c7b44cb..b042c59 100644
--- a/swh/model/tests/test_collections.py
+++ b/swh/model/tests/test_collections.py
@@ -1,50 +1,66 @@
 # Copyright (C) 2020 The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import pytest
 
 from swh.model.collections import ImmutableDict
 
 
 def test_immutabledict_empty():
     d = ImmutableDict()
 
     assert d == {}
     assert d != {"foo": "bar"}
 
     assert list(d) == []
     assert list(d.items()) == []
 
 
 def test_immutabledict_one_item():
     d = ImmutableDict({"foo": "bar"})
 
     assert d == {"foo": "bar"}
     assert d != {}
 
     assert d["foo"] == "bar"
     with pytest.raises(KeyError, match="bar"):
         d["bar"]
 
     assert list(d) == ["foo"]
     assert list(d.items()) == [("foo", "bar")]
 
 
+def test_immutabledict_from_iterable():
+    d1 = ImmutableDict()
+    d2 = ImmutableDict({"foo": "bar"})
+
+    assert ImmutableDict([]) == d1
+    assert ImmutableDict([("foo", "bar")]) == d2
+
+
+def test_immutabledict_from_immutabledict():
+    d1 = ImmutableDict()
+    d2 = ImmutableDict({"foo": "bar"})
+
+    assert ImmutableDict(d1) == d1
+    assert ImmutableDict(d2) == d2
+
+
 def test_immutabledict_immutable():
     d = ImmutableDict({"foo": "bar"})
 
     with pytest.raises(TypeError, match="item assignment"):
         d["bar"] = "baz"
 
     with pytest.raises(TypeError, match="item deletion"):
         del d["foo"]
 
 
 def test_immutabledict_copy_pop():
     d = ImmutableDict({"foo": "bar", "baz": "qux"})
 
     assert d.copy_pop("foo") == ("bar", ImmutableDict({"baz": "qux"}))
 
     assert d.copy_pop("not a key") == (None, d)