diff -r 6a454e7053a1 -r 220506bb213e mercurial/cmdutil.py
--- a/mercurial/cmdutil.py	Fri Nov 19 12:57:53 2021 -0800
+++ b/mercurial/cmdutil.py	Fri Nov 19 09:17:30 2021 -0800
@@ -2025,7 +2025,12 @@
                 similarity=sim / 100.0,
             )
         except error.PatchParseError as e:
-            raise error.InputError(pycompat.bytestr(e))
+            raise error.InputError(
+                pycompat.bytestr(e),
+                hint=_(
+                    b'check that whitespace in the patch has not been mangled'
+                ),
+            )
         except error.PatchApplicationError as e:
             if not partial:
                 raise error.StateError(pycompat.bytestr(e))
@@ -2086,7 +2091,12 @@
                     eolmode=None,
                 )
             except error.PatchParseError as e:
-                raise error.InputError(stringutil.forcebytestr(e))
+                raise error.InputError(
+                    stringutil.forcebytestr(e),
+                    hint=_(
+                        b'check that whitespace in the patch has not been mangled'
+                    ),
+                )
             except error.PatchApplicationError as e:
                 raise error.StateError(stringutil.forcebytestr(e))
             if opts.get(b'exact'):