diff --git a/pyfixest/estimation/FixestMulti_.py b/pyfixest/estimation/FixestMulti_.py
index ec68bf0f..8d62e91e 100644
--- a/pyfixest/estimation/FixestMulti_.py
+++ b/pyfixest/estimation/FixestMulti_.py
@@ -71,7 +71,8 @@ def __init__(
         self._reps = reps if use_compression else None
         self._seed = seed if use_compression else None
 
-        self._run_split = split or fsplit
+        self._run_split = split is not None or fsplit is not None
+        self._run_full = not (split and not fsplit)
 
         self._splitvar: Optional[str] = None
         if self._run_split:
@@ -82,8 +83,6 @@ def __init__(
         else:
             self._splitvar = None
 
-        self._run_full = not (split and not fsplit)
-
         data = _polars_to_pandas(data)
 
         if self._copy_data:
@@ -171,7 +170,7 @@ def _prepare_estimation(
 
         FML = FixestFormulaParser(fml)
         FML.set_fixest_multi_flag()
-        self._is_multiple_estimation = FML._is_multiple_estimation
+        self._is_multiple_estimation = FML._is_multiple_estimation or self._run_split
         self.FixestFormulaDict = FML.FixestFormulaDict
         self._method = estimation
         self._is_iv = FML.is_iv
@@ -231,9 +230,7 @@ def _estimate_all_models(
         _fixef_keys = list(FixestFormulaDict.keys())
 
         all_splits = (["all"] if _run_full else []) + (
-            _data[_splitvar].dropna().unique().tolist()
-            if _run_split is not None
-            else []
+            _data[_splitvar].dropna().unique().tolist() if _run_split else []
         )
 
         for sample_split_value in all_splits:
diff --git a/tests/test_vs_fixest.py b/tests/test_vs_fixest.py
index 72b755fb..4587cd08 100644
--- a/tests/test_vs_fixest.py
+++ b/tests/test_vs_fixest.py
@@ -11,6 +11,7 @@
 
 import pyfixest as pf
 from pyfixest.estimation.estimation import feols
+from pyfixest.estimation.FixestMulti_ import FixestMulti
 from pyfixest.utils.set_rpy2_path import update_r_paths
 from pyfixest.utils.utils import get_data, ssc
 
@@ -547,11 +548,6 @@ def test_single_fit_iv(
 @pytest.mark.parametrize(
     "fml_multi",
     [
-        ("Y ~X1"),
-        ("Y ~X1+X2"),
-        ("Y~X1|f1"),
-        ("Y~X1|f1+f2"),
-        ("Y~X2|f2+f3"),
         ("Y~ sw(X1, X2)"),
         ("Y~ sw(X1, X2) |f1 "),
         ("Y~ csw(X1, X2)"),
@@ -607,6 +603,7 @@ def test_multi_fit(N, seed, beta_type, error_type, dropna, fml_multi):
 
     try:
         pyfixest = feols(fml=fml_multi, data=data)
+        assert isinstance(pyfixest, FixestMulti)
     except ValueError as e:
         if "is not of type 'O' or 'category'" in str(e):
             data["f1"] = pd.Categorical(data.f1.astype(str))
@@ -680,6 +677,7 @@ def test_split_fit(N, seed, beta_type, error_type, dropna, fml_multi, split, fsp
 
     try:
         pyfixest = feols(fml=fml_multi, data=data, split=split, fsplit=fsplit)
+        assert isinstance(pyfixest, FixestMulti)
     except ValueError as e:
         if "is not of type 'O' or 'category'" in str(e):
             data["f1"] = pd.Categorical(data.f1.astype(str))