diff --git a/borgmatic/borg/create.py b/borgmatic/borg/create.py
index f3c3c69b..f459e51f 100644
--- a/borgmatic/borg/create.py
+++ b/borgmatic/borg/create.py
@@ -317,9 +317,7 @@ def check_all_source_directories_exist(source_directories):
         if not os.path.exists(source_directory)
     ]
     if missing_directories:
-        raise ValueError(
-            'Source directories do not exist: {}'.format(', '.join(missing_directories))
-        )
+        raise ValueError(f"Source directories do not exist: {', '.join(missing_directories)}")
 
 
 def create_archive(
@@ -509,7 +507,9 @@ def create_archive(
         )
     elif output_log_level is None:
         return execute_command_and_capture_output(
-            create_command, working_directory=working_directory, extra_environment=borg_environment,
+            create_command,
+            working_directory=working_directory,
+            extra_environment=borg_environment,
         )
     else:
         execute_command(
diff --git a/tests/unit/borg/test_create.py b/tests/unit/borg/test_create.py
index 3c4e4338..835ebed1 100644
--- a/tests/unit/borg/test_create.py
+++ b/tests/unit/borg/test_create.py
@@ -207,7 +207,6 @@ def test_make_exclude_flags_includes_exclude_patterns_filename_when_given():
 
 
 def test_make_exclude_flags_includes_exclude_from_filenames_when_in_config():
-
     exclude_flags = module.make_exclude_flags(
         location_config={'exclude_from': ['excludes', 'other']}
     )
@@ -1054,7 +1053,8 @@ def test_create_archive_with_compression_calls_borg_with_compression_parameters(
 
 
 @pytest.mark.parametrize(
-    'feature_available,option_flag', ((True, '--upload-ratelimit'), (False, '--remote-ratelimit')),
+    'feature_available,option_flag',
+    ((True, '--upload-ratelimit'), (False, '--remote-ratelimit')),
 )
 def test_create_archive_with_upload_rate_limit_calls_borg_with_upload_ratelimit_parameters(
     feature_available, option_flag
@@ -1189,7 +1189,8 @@ def test_create_archive_with_one_file_system_calls_borg_with_one_file_system_par
 
 
 @pytest.mark.parametrize(
-    'feature_available,option_flag', ((True, '--numeric-ids'), (False, '--numeric-owner')),
+    'feature_available,option_flag',
+    ((True, '--numeric-ids'), (False, '--numeric-owner')),
 )
 def test_create_archive_with_numeric_ids_calls_borg_with_numeric_ids_parameter(
     feature_available, option_flag
@@ -1291,7 +1292,12 @@ def test_create_archive_with_read_special_calls_borg_with_read_special_parameter
 
 @pytest.mark.parametrize(
     'option_name,option_value',
-    (('ctime', True), ('ctime', False), ('birthtime', True), ('birthtime', False),),
+    (
+        ('ctime', True),
+        ('ctime', False),
+        ('birthtime', True),
+        ('birthtime', False),
+    ),
 )
 def test_create_archive_with_basic_option_calls_borg_with_corresponding_parameter(
     option_name, option_value
@@ -1767,7 +1773,12 @@ def test_create_archive_with_progress_and_log_info_calls_borg_with_progress_para
     )
     flexmock(module.environment).should_receive('make_environment')
     flexmock(module).should_receive('execute_command').with_args(
-        ('borg', 'create') + REPO_ARCHIVE_WITH_PATHS + ('--info', '--progress',),
+        ('borg', 'create')
+        + REPO_ARCHIVE_WITH_PATHS
+        + (
+            '--info',
+            '--progress',
+        ),
         output_log_level=logging.INFO,
         output_file=module.DO_NOT_CAPTURE,
         borg_local_path='borg',
@@ -2530,3 +2541,27 @@ def test_create_archive_with_stream_processes_calls_borg_with_processes_and_read
         local_borg_version='1.2.3',
         stream_processes=processes,
     )
+
+
+def test_create_archive_with_non_existent_directory_and_source_directories_must_exist_raises_error():
+    """
+    If a source directory doesn't exist and source_directories_must_exist is True, raise an error.
+    """
+    flexmock(module.borgmatic.logger).should_receive('add_custom_log_levels')
+    flexmock(module.logging).ANSWER = module.borgmatic.logger.ANSWER
+    flexmock(module).should_receive('collect_borgmatic_source_directories').and_return([])
+    flexmock(module.os.path).should_receive('exists').and_return(False)
+
+    with pytest.raises(ValueError):
+        module.create_archive(
+            dry_run=False,
+            repository='repo',
+            location_config={
+                'source_directories': ['foo', 'bar'],
+                'repositories': ['repo'],
+                'exclude_patterns': None,
+                'source_directories_must_exist': True,
+            },
+            storage_config={},
+            local_borg_version='1.2.3',
+        )