diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
index 050e8901f98c..33c7d09a42c2 100644
--- a/lib/matplotlib/rcsetup.py
+++ b/lib/matplotlib/rcsetup.py
@@ -914,24 +914,40 @@ def _validate_linestyle(ls):
     A validator for all possible line styles, the named ones *and*
     the on-off ink sequences.
     """
-    # Named line style, like u'--' or u'solid'
-    if isinstance(ls, six.text_type):
-        return _validate_named_linestyle(ls)
-
-    # On-off ink (in points) sequence *of even length*.
+    # Look first for a valid named line style, like '--' or 'solid'
+    if isinstance(ls, six.string_types):
+        try:
+            return _validate_named_linestyle(ls)
+        except (UnicodeDecodeError, KeyError):
+            # On Python 2, string-like *ls*, like for example
+            # 'solid'.encode('utf-16'), may raise a unicode error.
+            raise ValueError("the linestyle string {!r} is not a valid "
+                             "string.".format(ls))
+
+    if isinstance(ls, (bytes, bytearray)):
+        # On Python 2, a string-like *ls* should already have lead to a
+        # successful return or to raising an exception. On Python 3, we have
+        # to manually raise an exception in the case of a byte-like *ls*.
+        # Otherwise, if *ls* is of even-length, it will be passed to the
+        # instance of validate_nseq_float, which will return an absurd on-off
+        # ink sequence...
+        raise ValueError("linestyle {!r} neither looks like an on-off ink "
+                         "sequence nor a valid string.".format(ls))
+
+    # Look for an on-off ink sequence (in points) *of even length*.
     # Offset is set to None.
     try:
         if len(ls) % 2 != 0:
-            # Expecting a sequence of even length
-            raise ValueError
+            raise ValueError("the linestyle sequence {!r} is not of even "
+                             "length.".format(ls))
+
         return (None, validate_nseq_float()(ls))
-    except (ValueError, TypeError):
-        # TypeError can be raised by wrong types passed to float()
-        # (called inside the instance of validate_nseq_float).
-        pass
 
-    raise ValueError("linestyle must be a string or " +
-                     "an even-length sequence of floats.")
+    except (ValueError, TypeError):
+        # TypeError can be raised inside the instance of validate_nseq_float,
+        # by wrong types passed to float(), like NoneType.
+        raise ValueError("linestyle {!r} is not a valid on-off ink "
+                         "sequence.".format(ls))
 
 
 # a map from key -> value, converter
diff --git a/lib/matplotlib/tests/test_rcparams.py b/lib/matplotlib/tests/test_rcparams.py
index 4e689f6b9c47..e84a90ee34cf 100644
--- a/lib/matplotlib/tests/test_rcparams.py
+++ b/lib/matplotlib/tests/test_rcparams.py
@@ -333,29 +333,45 @@ def generate_validator_testcases(valid):
                      ),
          'fail': (('aardvark', ValueError),
                   )
-         },
-         {'validator': _validate_linestyle,  # NB: case-insensitive
-         'success': (('-', '-'), ('solid', 'solid'),
-                     ('--', '--'), ('dashed', 'dashed'),
-                     ('-.', '-.'), ('dashdot', 'dashdot'),
-                     (':', ':'), ('dotted', 'dotted'),
-                     ('', ''), (' ', ' '),
-                     ('None', 'none'), ('none', 'none'),
-                     ('DoTtEd', 'dotted'),
-                     (['1.23', '4.56'], (None, [1.23, 4.56])),
-                     ([1.23, 456], (None, [1.23, 456.0])),
-                     ([1, 2, 3, 4], (None, [1.0, 2.0, 3.0, 4.0])),
-                     ),
-         'fail': (('aardvark', ValueError),  # not a valid string
-                  ((None, [1, 2]), ValueError),  # (offset, dashes) is not OK
-                  ((0, [1, 2]), ValueError),  # idem
-                  ((-1, [1, 2]), ValueError),  # idem
-                  ([1, 2, 3], ValueError),  # not a sequence of even length
-                  (1.23, ValueError)  # not a sequence
-                  )
          }
     )
 
+    # The behavior of _validate_linestyle depends on the version of Python.
+    # ASCII-compliant bytes arguments should pass on Python 2 because of the
+    # automatic conversion between bytes and strings. Python 3 does not
+    # perform such a conversion, so the same cases should raise an exception.
+    #
+    # Common cases:
+    ls_test = {'validator': _validate_linestyle,
+               'success': (('-', '-'), ('solid', 'solid'),
+                           ('--', '--'), ('dashed', 'dashed'),
+                           ('-.', '-.'), ('dashdot', 'dashdot'),
+                           (':', ':'), ('dotted', 'dotted'),
+                           ('', ''), (' ', ' '),
+                           ('None', 'none'), ('none', 'none'),
+                           ('DoTtEd', 'dotted'),  # case-insensitive
+                           (['1.23', '4.56'], (None, [1.23, 4.56])),
+                           ([1.23, 456], (None, [1.23, 456.0])),
+                           ([1, 2, 3, 4], (None, [1.0, 2.0, 3.0, 4.0])),
+                          ),
+               'fail': (('aardvark', ValueError),  # not a valid string
+                        ('dotted'.encode('utf-16'), ValueError),  # even on PY2
+                        ((None, [1, 2]), ValueError),  # (offset, dashes) != OK
+                        ((0, [1, 2]), ValueError),  # idem
+                        ((-1, [1, 2]), ValueError),  # idem
+                        ([1, 2, 3], ValueError),  # sequence with odd length
+                        (1.23, ValueError),  # not a sequence
+                       )
+                }
+    # Add some cases of bytes arguments that Python 2 can convert silently:
+    ls_bytes_args = (b'dotted', 'dotted'.encode('ascii'))
+    if six.PY3:
+        ls_test['fail'] += tuple((arg, ValueError) for arg in ls_bytes_args)
+    else:
+        ls_test['success'] += tuple((arg, 'dotted') for arg in ls_bytes_args)
+    # Update the validation test sequence.
+    validation_tests += (ls_test,)
+
     for validator_dict in validation_tests:
         validator = validator_dict['validator']
         if valid: