diff --git a/gersemi/runner.py b/gersemi/runner.py
index 8e73475..9240648 100644
--- a/gersemi/runner.py
+++ b/gersemi/runner.py
@@ -131,7 +131,7 @@ def run_task(
     return task(formatted_file)
 
 
-def consume_task_result(task_result: TaskResult, quiet: bool) -> Tuple[Path, int]:
+def consume_task_result(task_result: TaskResult, quiet: bool) -> Tuple[Path, int, bool]:
     if task_result.to_stdout != "":
         print_to_stdout(task_result.to_stdout)
 
@@ -142,7 +142,7 @@ def consume_task_result(task_result: TaskResult, quiet: bool) -> Tuple[Path, int
         if task_result.to_stderr != "":
             print_to_stderr(task_result.to_stderr)
 
-    return task_result.path, task_result.return_code
+    return task_result.path, task_result.return_code, (len(task_result.warnings) > 0)
 
 
 def create_pool(is_stdin_in_sources, num_workers):
@@ -195,7 +195,7 @@ def handle_already_formatted_files(
         consume_task_result(result, quiet)
         for result in map(execute, already_formatted_files)
     ]
-    return compute_error_code(code for _, code in results)
+    return compute_error_code(code for _, code, _ in results)
 
 
 def handle_files_to_format(
@@ -227,9 +227,13 @@ def handle_files_to_format(
         mode,
         cache,
         configuration_summary,
-        (path for path, code in results if code == SUCCESS and path != Path("-")),
+        (
+            path
+            for path, code, has_warnings in results
+            if code == SUCCESS and path != Path("-") and (not has_warnings)
+        ),
     )
-    return compute_error_code(code for _, code in results)
+    return compute_error_code(code for _, code, _ in results)
 
 
 def run(mode: Mode, configuration: Configuration, sources: Iterable[Path]):
diff --git a/gersemi/warnings.py b/gersemi/warnings.py
index 2d126e8..d243abe 100644
--- a/gersemi/warnings.py
+++ b/gersemi/warnings.py
@@ -1,5 +1,5 @@
 from dataclasses import dataclass
-from typing import Iterable, Tuple, Union
+from typing import Sequence, Tuple, Union
 
 
 Position = Tuple[int, int]
@@ -8,7 +8,7 @@
 @dataclass
 class UnknownCommandWarning:
     command_name: str
-    positions: Iterable[Position]
+    positions: Sequence[Position]
 
     def get_message(self, filepath: str) -> str:
         return "\n".join(
@@ -26,4 +26,4 @@ def get_message(self, filepath: str) -> str:
 
 
 FormatterWarning = Union[UnknownCommandWarning, WrongFormattingWarning]
-FormatterWarnings = Iterable[FormatterWarning]
+FormatterWarnings = Sequence[FormatterWarning]
diff --git a/tests/test_executable.py b/tests/test_executable.py
index 82ee8a1..b6f2747 100644
--- a/tests/test_executable.py
+++ b/tests/test_executable.py
@@ -901,20 +901,25 @@ def check_warnings(result, stderr):
 
 
 @pytest.mark.parametrize(
-    ["args"],
+    ["args", "check_cache"],
     [
-        ((),),
-        (("--check",),),
-        (("--in-place",),),
-        (("--diff",),),
+        ((), False),
+        (("--check",), True),
+        (("--in-place",), True),
+        (("--diff",), False),
     ],
 )
-def test_warn_about_unknown_commands(tmpdir, args):
-    with temporary_dir_copy(TESTS / "warn_about_unknown_commands") as copy:
-        cmakelists = Path(copy) / "CMakeLists.txt"
-        custom_command_definition = Path(copy) / "watch_movies.cmake"
+def test_warn_about_unknown_commands(tmpdir, args, check_cache):
+    original = TESTS / "warn_about_unknown_commands"
 
-        with_definition = gersemi(
+    with cache_tests(original) as (target, gersemi_, inspector):
+        if check_cache:
+            inspector.assert_that_has_no_tables()
+
+        cmakelists = Path(target) / "CMakeLists.txt"
+        custom_command_definition = Path(target) / "watch_movies.cmake"
+
+        with_definition = gersemi_(
             *args,
             cmakelists,
             "--definitions",
@@ -927,7 +932,17 @@ def test_warn_about_unknown_commands(tmpdir, args):
         )
         assert with_definition.stderr == "", with_definition.stderr
 
-        without_definition = gersemi(*args, cmakelists, cwd=tmpdir)
+        if check_cache:
+            inspector.assert_that_has_initialized_tables()
+            assert len(inspector.get_files()) > 0
+            assert len(inspector.get_formatted()) > 0
+
+    with cache_tests(original) as (target, gersemi_, inspector):
+        if check_cache:
+            inspector.assert_that_has_no_tables()
+
+        cmakelists = Path(target) / "CMakeLists.txt"
+        without_definition = gersemi_(*args, cmakelists, cwd=tmpdir)
         assert without_definition.returncode == 0, (
             without_definition.returncode,
             without_definition.stderr,
@@ -945,6 +960,11 @@ def test_warn_about_unknown_commands(tmpdir, args):
 """
         ), without_definition.stderr
 
+        if check_cache:
+            inspector.assert_that_has_initialized_tables()
+            assert len(inspector.get_files()) == 0
+            assert len(inspector.get_formatted()) == 0
+
 
 @pytest.mark.parametrize(
     ["args"],