diff --git a/README.md b/README.md
index 0283a0c..04f3e7e 100644
--- a/README.md
+++ b/README.md
@@ -105,6 +105,9 @@ Mars          3390         641.85
 
 ```
 
+An iterable of column labels, including a NumPy array, supplies literal
+labels such as `"firstrow"` or `"keys"`.
+
 If `headers="firstrow"`, then the first row of data is used:
 
 ```pycon
@@ -151,7 +154,9 @@ called row index. To add a similar column to any other type of table,
 pass `showindex="always"` or `showindex=True` argument to `tabulate()`.
 To suppress row indices for all types of data, pass `showindex="never"`
 or `showindex=False`. To add a custom row index column, pass
-`showindex=rowIDs`, where `rowIDs` is some iterable:
+`showindex=rowIDs`, where `rowIDs` is some iterable, such as a list,
+NumPy array, or pandas Index. Custom row indices replace a DataFrame's
+original index and do not inherit its name:
 
 ```pycon
 >>> print(tabulate([["F",24],["M",19]], showindex="always"))
diff --git a/tabulate/__init__.py b/tabulate/__init__.py
index 12a2950..e1ee6c2 100644
--- a/tabulate/__init__.py
+++ b/tabulate/__init__.py
@@ -1459,9 +1459,7 @@ def _normalize_tabular_data(tabular_data, headers, showindex="default"):
 
     """
 
-    try:
-        bool(headers)
-    except ValueError:  # numpy.ndarray, pandas.core.index.Index, ...
+    if not isinstance(headers, (str, dict)):
         headers = list(headers)
 
     err_msg = (
@@ -1469,6 +1467,7 @@ def _normalize_tabular_data(tabular_data, headers, showindex="default"):
         "like a list of lists or similar."
         "\nDid you forget a pair of extra [] or ',' in ()?"
     )
+    showindex_is_a_str = type(showindex) in [str, bytes]
     index = None
     if hasattr(tabular_data, "keys") and hasattr(tabular_data, "values"):
         # dict-like and pandas.DataFrame?
@@ -1483,7 +1482,11 @@ def _normalize_tabular_data(tabular_data, headers, showindex="default"):
         elif hasattr(tabular_data, "index"):
             # values is a property, has .index => it's likely a pandas.DataFrame (pandas 0.11.0)
             keys = list(tabular_data)
-            if showindex in ["default", "always", True] and tabular_data.index.name is not None:
+            if (
+                (showindex_is_a_str or not isinstance(showindex, (Sized, Iterable)))
+                and showindex in ["default", "always", True]
+                and tabular_data.index.name is not None
+            ):
                 if isinstance(tabular_data.index.name, list):
                     keys[:0] = tabular_data.index.name
                 else:
@@ -1590,7 +1593,6 @@ def _normalize_tabular_data(tabular_data, headers, showindex="default"):
     rows = [r if _is_separating_line(r) else list(r) for r in rows]
 
     # add or remove an index column
-    showindex_is_a_str = type(showindex) in [str, bytes]
     if showindex_is_a_str and showindex == "default" and index is not None:
         rows = _prepend_row_index(rows, index)
     elif isinstance(showindex, Sized) and not showindex_is_a_str:
diff --git a/test/test_dataframe_indices.py b/test/test_dataframe_indices.py
new file mode 100644
index 0000000..0279fac
--- /dev/null
+++ b/test/test_dataframe_indices.py
@@ -0,0 +1,66 @@
+"""DataFrame row-index options must not compare array-like values as scalars."""
+
+import pytest
+
+from tabulate import tabulate
+
+
+@pytest.mark.parametrize("index_type", ["array", "Index", "Series"])
+@pytest.mark.parametrize("index_name", [None, "original"])
+@pytest.mark.parametrize("row_ids", [[], [10, 20], [1], ["default"], ["always"], [True]])
+def test_dataframe_array_like_row_indices(index_type, index_name, row_ids):
+    numpy = pytest.importorskip("numpy")
+    pandas = pytest.importorskip("pandas")
+    frame = pandas.DataFrame({"value": range(len(row_ids))})
+    frame.index.name = index_name
+    factory = numpy.array if index_type == "array" else getattr(pandas, index_type)
+    indices = factory(row_ids)
+
+    expected = tabulate(frame, headers="keys", showindex=list(indices))
+    actual = tabulate(frame, headers="keys", showindex=indices)
+
+    assert actual == expected
+    assert "original" not in actual
+
+
+def test_dataframe_sequence_row_indices():
+    pandas = pytest.importorskip("pandas")
+    frame = pandas.DataFrame({"value": [1, 2]})
+    frame.index.name = "original"
+
+    class RowIndices:
+        def __len__(self):
+            return 2
+
+        def __getitem__(self, index):
+            return [10, 20][index]
+
+        def __eq__(self, other):
+            raise AssertionError("Custom row indices must not be compared to scalar modes")
+
+    assert tabulate(frame, headers="keys", showindex=RowIndices()) == tabulate(
+        frame, headers="keys", showindex=[10, 20]
+    )
+
+
+@pytest.mark.parametrize("showindex", ["default", "always", True, "never", False])
+def test_dataframe_scalar_row_index_options(showindex):
+    pandas = pytest.importorskip("pandas")
+    frame = pandas.DataFrame({"value": [1, 2]})
+    frame.index.name = "original"
+
+    actual = tabulate(frame, headers="keys", showindex=showindex)
+
+    assert ("original" in actual) == (showindex in ["default", "always", True])
+
+
+def test_dataframe_numpy_boolean_row_index_options():
+    numpy = pytest.importorskip("numpy")
+    pandas = pytest.importorskip("pandas")
+    frame = pandas.DataFrame({"value": [1, 2]})
+    frame.index.name = "original"
+
+    for showindex in (True, False):
+        assert tabulate(frame, headers="keys", showindex=numpy.bool_(showindex)) == tabulate(
+            frame, headers="keys", showindex=showindex
+        )
diff --git a/test/test_header_iterables.py b/test/test_header_iterables.py
new file mode 100644
index 0000000..bb82ca5
--- /dev/null
+++ b/test/test_header_iterables.py
@@ -0,0 +1,26 @@
+"""Iterable column labels must not be interpreted as scalar header modes."""
+
+import pytest
+
+from tabulate import tabulate
+
+
+@pytest.mark.parametrize("input_type", ["list", "numpy", "dict", "dataframe"])
+@pytest.mark.parametrize(
+    "labels", [["firstrow"], ["keys"], ["literal"], ["firstrow", "keys"], [], [0], [True]]
+)
+def test_numpy_array_column_labels(input_type, labels):
+    numpy = pytest.importorskip("numpy")
+    rows = [["keep first"], ["keep second"]]
+    if input_type == "numpy":
+        table = numpy.array(rows)
+    elif input_type == "dict":
+        table = {"column": [row[0] for row in rows]}
+    elif input_type == "dataframe":
+        pandas = pytest.importorskip("pandas")
+        table = pandas.DataFrame(rows)
+    else:
+        table = rows
+    headers = numpy.array(labels)
+
+    assert tabulate(table, headers=headers) == tabulate(table, headers=list(headers))