diff --git a/pandas/core/algorithms.py b/pandas/core/algorithms.py
index d74c5e66ea1a9..16bb92f3706ef 100644
--- a/pandas/core/algorithms.py
+++ b/pandas/core/algorithms.py
@@ -64,6 +64,10 @@ def _ensure_data(values, dtype=None):
 
     """
 
+    # short-circuit on object dtype requested
+    if is_object_dtype(dtype):
+        return _ensure_object(values), 'object', 'object'
+
     # we check some simple dtypes first
     try:
         if is_bool_dtype(values) or is_bool_dtype(dtype):
@@ -161,6 +165,7 @@ def _ensure_arraylike(values):
     """
     if not isinstance(values, (np.ndarray, ABCCategorical,
                                ABCIndexClass, ABCSeries)):
+        values = list(values)
         inferred = lib.infer_dtype(values)
         if inferred in ['mixed', 'string', 'unicode']:
             values = lib.list_to_object_array(values)
@@ -392,10 +397,9 @@ def isin(comps, values):
                         " to isin(), you passed a "
                         "[{0}]".format(type(values).__name__))
 
-    if not isinstance(values, (ABCIndex, ABCSeries, np.ndarray)):
-        values = lib.list_to_object_array(list(values))
-
+    comps = _ensure_arraylike(comps)
     comps, dtype, _ = _ensure_data(comps)
+    values = _ensure_arraylike(values)
     values, _, _ = _ensure_data(values, dtype=dtype)
 
     # GH11232