diff --git a/tests/test_metadata_serialization.py b/tests/test_metadata_serialization.py
index 1f5867d2ce..7b3894e3e7 100644
--- a/tests/test_metadata_serialization.py
+++ b/tests/test_metadata_serialization.py
@@ -304,6 +304,22 @@ def test_invalid_delegated_role_serialization(self, test_case_data: str):
             DelegatedRole.from_dict(copy.copy(case_dict))
 
 
+    invalid_delegations: DataSet = {
+        "duplicate role names": '{"keys": {"keyid" : {"keytype": "rsa", "scheme": "rsassa-pss-sha256", "keyval": {"public": "foo"}}}, \
+            "roles": [ \
+                {"keyids": ["keyid"], "name": "a", "paths": ["fn1", "fn2"], "terminating": false, "threshold": 3}, \
+                {"keyids": ["keyid2"], "name": "a", "paths": ["fn3"], "terminating": false, "threshold": 2}    \
+                ] \
+            }',
+    }
+
+    @run_sub_tests_with_dataset(invalid_delegations)
+    def test_invalid_delegation_serialization(self, test_case_data: str):
+        case_dict = json.loads(test_case_data)
+        with self.assertRaises(ValueError):
+            Delegations.from_dict(copy.deepcopy(case_dict))
+
+
     valid_delegations: DataSet = {
         "all":
             '{"keys": { \
diff --git a/tuf/api/metadata.py b/tuf/api/metadata.py
index fb4a1daf2c..dd59e82187 100644
--- a/tuf/api/metadata.py
+++ b/tuf/api/metadata.py
@@ -339,10 +339,7 @@ def verify_delegate(
                 raise ValueError(f"No delegation found for {delegated_role}")
 
             keys = self.signed.delegations.keys
-            roles = self.signed.delegations.roles
-            # Assume role names are unique in delegations.roles: #1426
-            # Find first role in roles with matching name (or None if no match)
-            role = next((r for r in roles if r.name == delegated_role), None)
+            role = self.signed.delegations.roles.get(delegated_role)
         else:
             raise TypeError("Call is valid only on delegator metadata")
 
@@ -1129,16 +1126,17 @@ class Delegations:
 
     Attributes:
         keys: Dictionary of keyids to Keys. Defines the keys used in 'roles'.
-        roles: List of DelegatedRoles that define which keys are required to
-            sign the metadata for a specific role. The roles order also
-            defines the order that role delegations are considered in.
+        roles: Ordered dictionary of role names to DelegatedRoles instances. It
+            defines which keys are required to sign the metadata for a specific
+            role. The roles order also defines the order that role delegations
+            are considered in.
         unrecognized_fields: Dictionary of all unrecognized fields.
     """
 
     def __init__(
         self,
         keys: Dict[str, Key],
-        roles: List[DelegatedRole],
+        roles: "OrderedDict[str, DelegatedRole]",
         unrecognized_fields: Optional[Mapping[str, Any]] = None,
     ) -> None:
         self.keys = keys
@@ -1153,17 +1151,19 @@ def from_dict(cls, delegations_dict: Dict[str, Any]) -> "Delegations":
         for keyid, key_dict in keys.items():
             keys_res[keyid] = Key.from_dict(keyid, key_dict)
         roles = delegations_dict.pop("roles")
-        roles_res = []
+        roles_res: "OrderedDict[str, DelegatedRole]" = OrderedDict()
         for role_dict in roles:
             new_role = DelegatedRole.from_dict(role_dict)
-            roles_res.append(new_role)
+            if new_role.name in roles_res:
+                raise ValueError(f"Duplicate role {new_role.name}")
+            roles_res[new_role.name] = new_role
         # All fields left in the delegations_dict are unrecognized.
         return cls(keys_res, roles_res, delegations_dict)
 
     def to_dict(self) -> Dict[str, Any]:
         """Returns the dict representation of self."""
         keys = {keyid: key.to_dict() for keyid, key in self.keys.items()}
-        roles = [role_obj.to_dict() for role_obj in self.roles]
+        roles = [role_obj.to_dict() for role_obj in self.roles.values()]
         return {
             "keys": keys,
             "roles": roles,
diff --git a/tuf/ngclient/updater.py b/tuf/ngclient/updater.py
index a3c7189d75..87290bf0aa 100644
--- a/tuf/ngclient/updater.py
+++ b/tuf/ngclient/updater.py
@@ -420,7 +420,7 @@ def _preorder_depth_first_walk(
                 child_roles_to_visit = []
                 # NOTE: This may be a slow operation if there are many
                 # delegated roles.
-                for child_role in role_metadata.delegations.roles:
+                for child_role in role_metadata.delegations.roles.values():
                     if child_role.is_delegated_path(target_filepath):
                         logger.debug("Adding child role %s", child_role.name)