diff --git a/src/ahriman/application/handlers/handler.py b/src/ahriman/application/handlers/handler.py
index 6886b08f..23a582ba 100644
--- a/src/ahriman/application/handlers/handler.py
+++ b/src/ahriman/application/handlers/handler.py
@@ -23,7 +23,7 @@ import argparse
 import logging
 
 from multiprocessing import Pool
-from typing import List, Type
+from typing import Set, Type
 
 from ahriman.application.lock import Lock
 from ahriman.core.configuration import Configuration
@@ -63,11 +63,11 @@ class Handler:
         architectures = cls.extract_architectures(args)
         with Pool(len(architectures)) as pool:
             result = pool.starmap(
-                cls._call, [(args, architecture) for architecture in set(architectures)])
+                cls._call, [(args, architecture) for architecture in architectures])
         return 0 if all(result) else 1
 
     @classmethod
-    def extract_architectures(cls: Type[Handler], args: argparse.Namespace) -> List[str]:
+    def extract_architectures(cls: Type[Handler], args: argparse.Namespace) -> Set[str]:
         """
         get known architectures
         :param args: command line args
@@ -76,13 +76,16 @@ class Handler:
         if args.architecture is None:
             raise MissingArchitecture(args.command)
         if args.architecture:
-            architectures: List[str] = args.architecture  # avoid mypy warning
-            return architectures
+            return set(args.architecture)
 
         config = Configuration()
         config.load(args.configuration)
         root = config.getpath("repository", "root")
-        return RepositoryPaths.known_architectures(root)
+        architectures = RepositoryPaths.known_architectures(root)
+
+        if not architectures:
+            raise MissingArchitecture(args.command)
+        return architectures
 
     @classmethod
     def run(cls: Type[Handler], args: argparse.Namespace, architecture: str, configuration: Configuration) -> None:
diff --git a/src/ahriman/models/repository_paths.py b/src/ahriman/models/repository_paths.py
index 9eaa398a..12c6ebfa 100644
--- a/src/ahriman/models/repository_paths.py
+++ b/src/ahriman/models/repository_paths.py
@@ -21,7 +21,7 @@ from __future__ import annotations
 
 from dataclasses import dataclass
 from pathlib import Path
-from typing import List, Type
+from typing import Set, Type
 
 
 @dataclass
@@ -79,18 +79,18 @@ class RepositoryPaths:
         return self.root / "sources" / self.architecture
 
     @classmethod
-    def known_architectures(cls: Type[RepositoryPaths], root: Path) -> List[str]:
+    def known_architectures(cls: Type[RepositoryPaths], root: Path) -> Set[str]:
         """
         get known architectures
         :param root: repository root
         :return: list of architectures for which tree is created
         """
         paths = cls(root, "")
-        return [
+        return {
             path.name
             for path in paths.repository.iterdir()
             if path.is_dir()
-        ]
+        }
 
     def create_tree(self) -> None:
         """
diff --git a/tests/ahriman/application/handlers/test_handler.py b/tests/ahriman/application/handlers/test_handler.py
index 78d91d25..cd7c9efa 100644
--- a/tests/ahriman/application/handlers/test_handler.py
+++ b/tests/ahriman/application/handlers/test_handler.py
@@ -57,12 +57,18 @@ def test_extract_architectures(args: argparse.Namespace, mocker: MockerFixture)
     known_architectures_mock.assert_called_once()
 
 
-def test_extract_architectures_specified(args: argparse.Namespace) -> None:
+def test_extract_architectures_empty(args: argparse.Namespace, mocker: MockerFixture) -> None:
     """
-    must return architecture list if it has been specified
+    must raise exception if no available architectures found
     """
-    architectures = args.architecture = ["i686", "x86_64"]
-    assert Handler.extract_architectures(args) == architectures
+    args.architecture = []
+    args.command = "config"
+    args.configuration = Path("")
+    mocker.patch("ahriman.core.configuration.Configuration.getpath")
+    mocker.patch("ahriman.models.repository_paths.RepositoryPaths.known_architectures", return_value=set())
+
+    with pytest.raises(MissingArchitecture):
+        Handler.extract_architectures(args)
 
 
 def test_extract_architectures_exception(args: argparse.Namespace) -> None:
@@ -75,6 +81,14 @@ def test_extract_architectures_exception(args: argparse.Namespace) -> None:
         Handler.extract_architectures(args)
 
 
+def test_extract_architectures_specified(args: argparse.Namespace) -> None:
+    """
+    must return architecture list if it has been specified
+    """
+    architectures = args.architecture = ["i686", "x86_64"]
+    assert Handler.extract_architectures(args) == set(architectures)
+
+
 def test_run(args: argparse.Namespace, configuration: Configuration) -> None:
     """
     must raise NotImplemented for missing method