diff --git a/lib/matplotlib/hatch.py b/lib/matplotlib/hatch.py
index 9ec88776cfd3..992df2d90bb7 100644
--- a/lib/matplotlib/hatch.py
+++ b/lib/matplotlib/hatch.py
@@ -2,7 +2,6 @@
 
 import numpy as np
 
-from matplotlib import _api
 from matplotlib.path import Path
 
 
@@ -180,20 +179,18 @@ def __init__(self, hatch, density):
 
 
 def _validate_hatch_pattern(hatch):
-    valid_hatch_patterns = set(r'-+|/\xXoO.*')
+    valid_hatch_patterns = set(r'-+|/\\xXoO.*')
     if hatch is not None:
+        if not isinstance(hatch, str):
+            raise ValueError("Hatch pattern must be a string")
         invalids = set(hatch).difference(valid_hatch_patterns)
         if invalids:
             valid = ''.join(sorted(valid_hatch_patterns))
             invalids = ''.join(sorted(invalids))
-            _api.warn_deprecated(
-                '3.4',
-                removal='3.9',  # one release after custom hatches (#20690)
-                message=f'hatch must consist of a string of "{valid}" or '
-                        'None, but found the following invalid values '
-                        f'"{invalids}". Passing invalid values is deprecated '
-                        'since %(since)s and will become an error %(removal)s.'
-            )
+            message = f"""Unknown hatch symbol(s): {invalids}.
+                    Hatch must consist of a string of {valid}"""
+            raise ValueError(message)
+    return hatch
 
 
 def get_path(hatchpattern, density=6):
diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
index 38d4606024d3..f9d05a95e642 100644
--- a/lib/matplotlib/rcsetup.py
+++ b/lib/matplotlib/rcsetup.py
@@ -22,6 +22,7 @@
 
 import numpy as np
 
+from matplotlib.hatch import _validate_hatch_pattern
 from matplotlib import _api, cbook
 from matplotlib.cbook import ls_mapper
 from matplotlib.colors import Colormap, is_color_like
@@ -592,19 +593,7 @@ def _validate_int_greaterequal0(s):
         raise RuntimeError(f'Value must be >=0; got {s}')
 
 
-def validate_hatch(s):
-    r"""
-    Validate a hatch pattern.
-    A hatch pattern string can have any sequence of the following
-    characters: ``\ / | - + * . x o O``.
-    """
-    if not isinstance(s, str):
-        raise ValueError("Hatch pattern must be a string")
-    _api.check_isinstance(str, hatch_pattern=s)
-    unknown = set(s) - {'\\', '/', '|', '-', '+', '*', '.', 'x', 'o', 'O'}
-    if unknown:
-        raise ValueError("Unknown hatch symbol(s): %s" % list(unknown))
-    return s
+validate_hatch = _validate_hatch_pattern
 
 
 validate_hatchlist = _listify_validator(validate_hatch)
diff --git a/lib/matplotlib/tests/test_rcparams.py b/lib/matplotlib/tests/test_rcparams.py
index 65cd823f13a9..4635c6b5f44e 100644
--- a/lib/matplotlib/tests/test_rcparams.py
+++ b/lib/matplotlib/tests/test_rcparams.py
@@ -311,10 +311,9 @@ def generate_validator_testcases(valid):
          },
         {'validator': validate_hatch,
          'success': (('--|', '--|'), ('\\oO', '\\oO'),
-                     ('/+*/.x', '/+*/.x'), ('', '')),
+                     ('/+*/.xX', '/+*/.xX'), ('', '')),
          'fail': (('--_', ValueError),
-                  (8, ValueError),
-                  ('X', ValueError)),
+                  (8, ValueError),),
          },
         {'validator': validate_colorlist,
          'success': (('r,g,b', ['r', 'g', 'b']),