diff --git a/docs/source/internal/utils.rst b/docs/source/internal/utils.rst
index 31e0d39..fed9a47 100644
--- a/docs/source/internal/utils.rst
+++ b/docs/source/internal/utils.rst
@@ -25,13 +25,8 @@
 
     "E121,W123,F904"
     "E121,\nW123,\nF804"
-    "E121,\n\tW123,\n\tF804"
-
-Or it will take a list of strings (potentially with whitespace) such as
-
-.. code-block:: python
-
-    ["   E121\n", "\t\nW123   ", "\n\tF904\n    "]
+    " E121,\n\tW123,\n\tF804 "
+    " E121\n\tW123 \n\tF804"
 
 And converts it to a list that looks as follows
 
@@ -50,9 +45,9 @@ path if the string has a ``/`` in it. It also removes trailing ``/``\ s.
 
 .. autofunction:: flake8.utils.normalize_paths
 
-This function utilizes :func:`~flake8.utils.parse_comma_separated_list` and
-:func:`~flake8.utils.normalize_path` to normalize its input to a list of
-strings that should be paths.
+This function utilizes :func:`~flake8.utils.normalize_path` to normalize a
+sequence of paths.  See :func:`~flake8.utils.normalize_path` for what defines a
+normalized path.
 
 .. autofunction:: flake8.utils.stdin_get_value
 
diff --git a/src/flake8/options/manager.py b/src/flake8/options/manager.py
index 5d21127..cf94927 100644
--- a/src/flake8/options/manager.py
+++ b/src/flake8/options/manager.py
@@ -2,7 +2,7 @@
 import collections
 import logging
 import optparse  # pylint: disable=deprecated-module
-from typing import Any, Callable, Dict, List, Optional, Set
+from typing import Dict, List, Optional, Set
 
 from flake8 import utils
 
@@ -142,14 +142,17 @@ class Option(object):
 
     def normalize(self, value, *normalize_args):
         """Normalize the value based on the option configuration."""
+        if self.comma_separated_list and isinstance(
+            value, utils.string_types
+        ):
+            value = utils.parse_comma_separated_list(value)
+
         if self.normalize_paths:
-            # Decide whether to parse a list of paths or a single path
-            normalize = utils.normalize_path  # type: Callable[..., Any]
-            if self.comma_separated_list:
-                normalize = utils.normalize_paths
-            return normalize(value, *normalize_args)
-        elif self.comma_separated_list:
-            return utils.parse_comma_separated_list(value)
+            if isinstance(value, list):
+                value = utils.normalize_paths(value, *normalize_args)
+            else:
+                value = utils.normalize_path(value, *normalize_args)
+
         return value
 
     def normalize_from_setuptools(self, value):
diff --git a/src/flake8/utils.py b/src/flake8/utils.py
index 02f0607..92fec71 100644
--- a/src/flake8/utils.py
+++ b/src/flake8/utils.py
@@ -24,11 +24,11 @@ string_types = (str, type(u""))
 
 
 def parse_comma_separated_list(value, regexp=COMMA_SEPARATED_LIST_RE):
-    # type: (Union[Sequence[str], str], Pattern[str]) -> List[str]
+    # type: (str, Pattern[str]) -> List[str]
     """Parse a comma-separated list.
 
     :param value:
-        String or list of strings to be parsed and normalized.
+        String to be parsed and normalized.
     :param regexp:
         Compiled regular expression used to split the value when it is a
         string.
@@ -39,13 +39,10 @@ def parse_comma_separated_list(value, regexp=COMMA_SEPARATED_LIST_RE):
     :rtype:
         list
     """
-    if not value:
-        return []
+    assert isinstance(value, string_types), value  # nosec (for bandit)
 
-    if isinstance(value, string_types):
-        value = regexp.split(value)
-
-    item_gen = (item.strip() for item in value)
+    separated = regexp.split(value)
+    item_gen = (item.strip() for item in separated)
     return [item for item in item_gen if item]
 
 
@@ -158,17 +155,16 @@ def parse_files_to_codes_mapping(value_):  # noqa: C901
 
 
 def normalize_paths(paths, parent=os.curdir):
-    # type: (Union[Sequence[str], str], str) -> List[str]
-    """Parse a comma-separated list of paths.
+    # type: (Sequence[str], str) -> List[str]
+    """Normalize a list of paths relative to a parent directory.
 
     :returns:
         The normalized paths.
     :rtype:
         [str]
     """
-    return [
-        normalize_path(p, parent) for p in parse_comma_separated_list(paths)
-    ]
+    assert isinstance(paths, list), paths  # nosec (for bandit)
+    return [normalize_path(p, parent) for p in paths]
 
 
 def normalize_path(path, parent=os.curdir):
diff --git a/tests/unit/test_utils.py b/tests/unit/test_utils.py
index 20c5fb9..151a76d 100644
--- a/tests/unit/test_utils.py
+++ b/tests/unit/test_utils.py
@@ -22,11 +22,7 @@ RELATIVE_PATHS = ["flake8", "pep8", "pyflakes", "mccabe"]
     ("E123,W234,,E206,,", ["E123", "W234", "E206"]),
     ("E123, W234,, E206,,", ["E123", "W234", "E206"]),
     ("E123,,W234,,E206,,", ["E123", "W234", "E206"]),
-    (["E123", "W234", "E206"], ["E123", "W234", "E206"]),
-    (["E123", "\n\tW234", "\n    E206"], ["E123", "W234", "E206"]),
-    (["E123", "\n\tW234", "\n    E206", "\n"], ["E123", "W234", "E206"]),
-    (["E123", "\n\tW234", "", "\n    E206", "\n"], ["E123", "W234", "E206"]),
-    (["E123", "\n\tW234", "", "\n    E206", ""], ["E123", "W234", "E206"]),
+    ("", []),
 ])
 def test_parse_comma_separated_list(value, expected):
     """Verify that similar inputs produce identical outputs."""
@@ -132,14 +128,13 @@ def test_normalize_path(value, expected):
 
 
 @pytest.mark.parametrize("value,expected", [
-    ("flake8,pep8,pyflakes,mccabe", ["flake8", "pep8", "pyflakes", "mccabe"]),
-    ("flake8,\n\tpep8,\n  pyflakes,\n\n    mccabe",
+    (["flake8", "pep8", "pyflakes", "mccabe"],
         ["flake8", "pep8", "pyflakes", "mccabe"]),
-    ("../flake8,../pep8,../pyflakes,../mccabe",
+    (["../flake8", "../pep8", "../pyflakes", "../mccabe"],
         [os.path.abspath("../" + p) for p in RELATIVE_PATHS]),
 ])
 def test_normalize_paths(value, expected):
-    """Verify we normalize comma-separated paths provided to the tool."""
+    """Verify we normalizes a sequence of paths provided to the tool."""
     assert utils.normalize_paths(value) == expected