diff --git a/swh/model/model.py b/swh/model/model.py
--- a/swh/model/model.py
+++ b/swh/model/model.py
@@ -772,6 +772,11 @@
     perms = attr.ib(type=int, validator=type_validator(), converter=int, repr=oct)
     """Usually one of the values of `swh.model.from_disk.DentryPerms`."""
 
+    @name.validator
+    def check_name(self, attribute, value):
+        if b"/" in value:
+            raise ValueError("{value!r} is not a valid directory entry name.")
+
 
 @attr.s(frozen=True, slots=True)
 class Directory(HashableObject, BaseModel):
@@ -784,6 +789,16 @@
         git_object = git_objects.directory_git_object(self)
         return hashlib.new("sha1", git_object).digest()
 
+    @entries.validator
+    def check_entries(self, attribute, value):
+        seen = set()
+        for entry in value:
+            if entry.name in seen:
+                raise ValueError(
+                    "{self.swhid()} has duplicated entry name: {entry.name!r}"
+                )
+            seen.add(entry.name)
+
     @classmethod
     def from_dict(cls, d):
         d = d.copy()
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
@@ -24,6 +24,7 @@
     BaseModel,
     Content,
     Directory,
+    DirectoryEntry,
     MetadataAuthority,
     MetadataAuthorityType,
     MetadataFetcher,
@@ -737,6 +738,30 @@
         )
 
 
+# Directory
+
+
+def test_directory_entry_name_validation():
+    with pytest.raises(ValueError, match="valid directory entry name."):
+        DirectoryEntry(name=b"foo/", type="dir", target=b"\x00" * 20, perms=0),
+
+
+def test_directory_duplicate_entry_name():
+    entries = (
+        DirectoryEntry(name=b"foo", type="file", target=b"\x00" * 20, perms=0),
+        DirectoryEntry(name=b"foo", type="dir", target=b"\x01" * 20, perms=1),
+    )
+    with pytest.raises(ValueError, match="duplicated entry name"):
+        Directory(entries=entries)
+
+    entries = (
+        DirectoryEntry(name=b"foo", type="file", target=b"\x00" * 20, perms=0),
+        DirectoryEntry(name=b"foo", type="file", target=b"\x00" * 20, perms=0),
+    )
+    with pytest.raises(ValueError, match="duplicated entry name"):
+        Directory(entries=entries)
+
+
 # Revision