diff --git a/miceforest/imputed_data.py b/miceforest/imputed_data.py
index 4e59341..dcae1fc 100644
--- a/miceforest/imputed_data.py
+++ b/miceforest/imputed_data.py
@@ -31,15 +31,10 @@ def __init__(
             self.working_data.index, RangeIndex
         ), "Please reset the index on the dataframe"
 
-        column_names = []
-        pd_dtypes_orig = {}
-        for col, series in self.working_data.items():
-            assert isinstance(col, str), "column names must be strings"
-            assert (
-                series.dtype.name != "object"
-            ), "convert object dtypes to something else"
-            column_names.append(col)
-            pd_dtypes_orig[col] = series.dtype.name
+        column_names = self.working_data.columns
+        assert np.all(
+            [isinstance(col, str) for col in column_names]
+        ), "Column names must be strings"
 
         self.column_names = column_names
         pd_dtypes_orig = self.working_data.dtypes
@@ -91,6 +86,18 @@ def __init__(
             col for col in self.modeled_variables if col in self.vars_with_any_missing
         ]
 
+        # This should be all variables in the schema, not all variables in the dataset.
+        self.all_var_in_schema = set(
+            self.modeled_variables
+            + [y for x in self.variable_schema.values() for y in x]
+        )
+
+        for col in self.all_var_in_schema:
+            assert pd_dtypes_orig[col].name != "object", (
+                "Cannot model an object column, please convert to int or categorical, or "
+                "specify a variable_schema that does not use the object column."
+            )
+
         if random_seed_array is not None:
             assert isinstance(random_seed_array, np.ndarray)
             assert (
diff --git a/pyproject.toml b/pyproject.toml
index 19ae41f..2902c39 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,7 +1,7 @@
 [project]
 name = "miceforest"
 license = "MIT"
-version = "6.0.4"
+version = "6.0.5"
 description = "Multiple Imputation by Chained Equations with LightGBM"
 authors = [{name="Sam Von Wilson"}]
 readme = "README.md"
diff --git a/tests/test_ImputationKernel.py b/tests/test_ImputationKernel.py
index 609fbe1..7a21ea8 100644
--- a/tests/test_ImputationKernel.py
+++ b/tests/test_ImputationKernel.py
@@ -368,3 +368,36 @@ def test_complex():
         mean_match_strategy=mixed_mms,
         save_all_iterations_data=True,
     )
+
+
+def test_object_column():
+
+    # Customize everything.
+    vs = {
+        "sl": ["ws", "pl", "pw", "sp", "bi"],
+        "ws": ["sl"],
+        "pl": ["sp", "bi"],
+        # 'sp': ['sl', 'ws', 'pl', 'pw', 'bc'], # Purposely don't train a variable that does have missing values
+        "pw": ["sl", "ws", "pl", "sp", "bi"],
+        "bi": ["ws", "pl", "sp"],
+        "ui8": ["sp", "ws"],
+    }
+    mmc = {"sl": 4, "ws": 0, "bi": 5}
+    ds = {"sl": int(iris_amp.shape[0] / 2), "ws": 50}
+
+    iris_amp["obj_col"] = iris_amp["sl"].astype("object")
+
+    imputed_var_names = list(vs)
+    non_imputed_var_names = [c for c in iris_amp if c not in imputed_var_names]
+    kernel = mf.ImputationKernel(
+        data=iris_amp,
+        num_datasets=2,
+        variable_schema=vs,
+        mean_match_candidates=mmc,
+        data_subset=ds,
+        mean_match_strategy="normal",
+        save_all_iterations_data=True,
+    )
+
+    assert "obj_col" not in kernel.variable_schema
+    assert "obj_col" not in kernel.all_var_in_schema