diff --git a/dias/rewriter.py b/dias/rewriter.py
index bc9e349..66397eb 100644
--- a/dias/rewriter.py
+++ b/dias/rewriter.py
@@ -372,12 +372,24 @@ def sort_head(called_on, by: str | None, n: int, asc: bool, orig: Callable):
     req_ty = pd.Series
     opt_func_obj = functools.partial(getattr(req_ty, func), n=n)
   
-  if type(called_on) == req_ty:
-    return opt_func_obj(self=called_on)
+  if type(called_on) != req_ty:
+    assert isinstance(orig, types.LambdaType)
+    return orig(called_on)
+
+  # nsmallest() errors on columns of dtype object, while sort_values() doesn't
+  if by is None:
+    assert type(called_on) == pd.Series
+    ser = called_on
   else:
+    assert type(called_on) == pd.DataFrame
+    ser = called_on[by]
+  if ser.dtype == object:
     assert isinstance(orig, types.LambdaType)
     return orig(called_on)
 
+  return opt_func_obj(self=called_on)
+  
+
 def substr_search_apply(ser, needle: str, orig: Callable):
   if type(ser) == pd.Series:
     ls = ser.tolist()
diff --git a/tests/sort_head-object.ipynb b/tests/sort_head-object.ipynb
new file mode 100644
index 0000000..e145608
--- /dev/null
+++ b/tests/sort_head-object.ipynb
@@ -0,0 +1,75 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import pandas as pd\n",
+    "import numpy as np\n",
+    "import dias.rewriter"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "df = pd.read_csv('titanic.csv')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# DIAS_DISABLE\n",
+    "defa = df['Name'].sort_values().head(4)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "our = df['Name'].sort_values().head(4)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# Convert to list so that we don't take account of the index. See correctness note in sort_head.ipynb\n",
+    "comp = [x == y for x, y in zip(our.tolist(), defa.tolist())]\n",
+    "assert all(comp)"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "base",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.9.13"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 2
+}
diff --git a/tests/sort_head-object.json b/tests/sort_head-object.json
new file mode 100644
index 0000000..6f2184a
--- /dev/null
+++ b/tests/sort_head-object.json
@@ -0,0 +1,24 @@
+{
+  "cells": [
+    {
+      "raw": "\ndf = pd.read_csv('titanic.csv')\n",
+      "modified": "df = pd.read_csv('titanic.csv')\n",
+      "patts-hit": {},
+      "rewritten-exec-time": 3.460375
+    },
+    {
+      "raw": "\n# DIAS_VERBOSE\nour = df['Name'].sort_values().head(4)\n",
+      "modified": "our = dias.rewriter.sort_head(called_on=df['Name'], by=None, n=4, asc=True,\n    orig=lambda _DIAS_x: _DIAS_x.sort_values().head(4))\n",
+      "patts-hit": {
+          "SortHead": 1
+      },
+      "rewritten-exec-time": 374.231
+    },
+    {
+      "raw": "\n# Convert to list so that we don't take account of the index. See correctness note in sort_head.ipynb\ncomp = [x == y for x, y in zip(our.tolist(), defa.tolist())]\nassert all(comp)\n",
+      "modified": "comp = [(x == y) for x, y in zip(our.tolist(), defa.tolist())]\nassert all(comp)\n",
+      "patts-hit": {},
+      "rewritten-exec-time": 7.40225
+    }
+  ]
+}
\ No newline at end of file