diff --git a/faircode/strategies.py b/faircode/strategies.py
index 2ec9342..c47b189 100644
--- a/faircode/strategies.py
+++ b/faircode/strategies.py
@@ -99,7 +99,9 @@ def strategy_features(strategy: str, core: list, proxies: list, protected: list)
         return list(dict.fromkeys(core + proxies + protected))
     if strategy == "unawareness":
         return list(dict.fromkeys(core + proxies))
-    return list(core)  # unawareness_proxy_removal, in_processing, post_processing
+    if strategy in ("unawareness_proxy_removal", "in_processing", "post_processing"):
+        return list(dict.fromkeys(core))
+    raise ValueError(f"unknown strategy: {strategy!r}")
 
 
 def fit_in_processing(base_model, X_train, y_train, sensitive_train):
diff --git a/tests/test_strategies.py b/tests/test_strategies.py
index 58178e1..d89b721 100644
--- a/tests/test_strategies.py
+++ b/tests/test_strategies.py
@@ -65,6 +65,16 @@ def test_strategy_features_deduplicates_overlapping_names():
     assert set(cols) == {"a", "b", "c"}
 
 
+def test_strategy_features_raises_on_unknown_strategy():
+    with pytest.raises(ValueError, match="unknown strategy: 'in_procesing'"):
+        strategy_features("in_procesing", CORE, PROXIES, PROTECTED)
+
+
+def test_strategy_features_raises_on_empty_string():
+    with pytest.raises(ValueError, match="unknown strategy: ''"):
+        strategy_features("", CORE, PROXIES, PROTECTED)
+
+
 # ── encode_features ──────────────────────────────────────────────────────────
 def test_encode_features_passes_numeric_columns_through():
     df = pd.DataFrame({"age": [20.0, 30.0, 40.0]})