diff --git a/backend/app/core/config.py b/backend/app/core/config.py
index 6862aac..18d5afa 100644
--- a/backend/app/core/config.py
+++ b/backend/app/core/config.py
@@ -40,6 +40,12 @@ class Settings(BaseSettings):
     )
     algorithm: str = "HS256"
     access_token_expire_minutes: int = 30
+    master_feed_limit: int = Field(
+        100,
+        validation_alias=AliasChoices(
+            "MASTER_FEED_LIMIT", "LETTERFEED_MASTER_FEED_LIMIT"
+        ),
+    )
 
 
 settings = Settings()
diff --git a/backend/app/services/feed_generator.py b/backend/app/services/feed_generator.py
index de036a9..f1ffa2a 100644
--- a/backend/app/services/feed_generator.py
+++ b/backend/app/services/feed_generator.py
@@ -77,7 +77,7 @@ def generate_feed(db: Session, feed_identifier: str):
 
 def generate_master_feed(db: Session):
     """Generate a master Atom feed for all newsletters."""
-    entries = get_all_entries(db)
+    entries = get_all_entries(db, limit=settings.master_feed_limit)
 
     feed_url = f"{settings.app_base_url}/feeds/all"
 
diff --git a/backend/app/tests/services/test_feed_generator.py b/backend/app/tests/services/test_feed_generator.py
new file mode 100644
index 0000000..f5f9abc
--- /dev/null
+++ b/backend/app/tests/services/test_feed_generator.py
@@ -0,0 +1,49 @@
+from unittest.mock import MagicMock, patch
+
+import pytest
+from feedgen.feed import FeedGenerator
+
+from app.services.feed_generator import generate_master_feed
+
+
+@pytest.fixture
+def mock_db_session():
+    """Fixture for a mock database session."""
+    return MagicMock()
+
+
+@patch("app.services.feed_generator.settings")
+def test_generate_master_feed_respects_limit(mock_settings, mock_db_session):
+    """Test that the master feed generation respects the MASTER_FEED_LIMIT."""
+    # Arrange
+    limit = 5
+    mock_settings.master_feed_limit = limit
+
+    # Create more mock entries than the limit
+    mock_entries = [MagicMock() for _ in range(limit + 5)]
+
+    with (
+        patch(
+            "app.services.feed_generator.get_all_entries", return_value=mock_entries
+        ) as mock_get_all_entries,
+        patch(
+            "app.services.feed_generator._create_feed_generator"
+        ) as mock_create_feed_generator,
+        patch(
+            "app.services.feed_generator._add_entries_to_feed"
+        ) as mock_add_entries_to_feed,
+    ):
+        mock_fg = MagicMock(spec=FeedGenerator)
+        mock_create_feed_generator.return_value = mock_fg
+        mock_fg.atom_str.return_value = "fake_atom_string"
+
+        # Act
+        result = generate_master_feed(mock_db_session)
+
+        # Assert
+        mock_get_all_entries.assert_called_once_with(mock_db_session, limit=limit)
+        mock_create_feed_generator.assert_called_once()
+        mock_add_entries_to_feed.assert_called_once_with(
+            mock_fg, mock_entries, is_master_feed=True
+        )
+        assert result == "fake_atom_string"
diff --git a/backend/pyproject.toml b/backend/pyproject.toml
index d2d4762..5bbf51f 100644
--- a/backend/pyproject.toml
+++ b/backend/pyproject.toml
@@ -50,6 +50,9 @@ lint.ignore = [
 [tool.ruff.lint.pydocstyle]
 convention = "google"
 
+[tool.ruff.lint.isort]
+known-first-party = ["app"]
+
 [tool.mypy]
 python_executable=".venv/bin/python"