diff --git a/llvm/docs/TestingGuide.rst b/llvm/docs/TestingGuide.rst
index c35e58bc53b67..08617933519fd 100644
--- a/llvm/docs/TestingGuide.rst
+++ b/llvm/docs/TestingGuide.rst
@@ -864,8 +864,9 @@ Additional substitutions can be defined as follows:
 - Lit configuration files (e.g., ``lit.cfg`` or ``lit.local.cfg``) can define
   substitutions for all tests in a test directory.  They do so by extending the
   substitution list, ``config.substitutions``.  Each item in the list is a tuple
-  consisting of a pattern and its replacement, which lit applies using python's
-  ``re.sub`` function.
+  consisting of a pattern and its replacement, which lit applies as plain text
+  (even if it contains sequences that python's ``re.sub`` considers to be
+  escape sequences).
 - To define substitutions within a single test file, lit supports the
   ``DEFINE:`` and ``REDEFINE:`` directives, described in detail below.  So that
   they have no effect on other test files, these directives modify a copy of the
diff --git a/llvm/utils/lit/lit/TestRunner.py b/llvm/utils/lit/lit/TestRunner.py
index da7fa86fd3917..7f312ad0768f0 100644
--- a/llvm/utils/lit/lit/TestRunner.py
+++ b/llvm/utils/lit/lit/TestRunner.py
@@ -1587,7 +1587,6 @@ def adjust_substitutions(self, substitutions):
         assert (
             not self.needs_continuation()
         ), "expected directive continuations to be parsed before applying"
-        value_repl = self.value.replace("\\", "\\\\")
         existing = [i for i, subst in enumerate(substitutions) if self.name in subst[0]]
         existing_res = "".join(
             "\nExisting pattern: " + substitutions[i][0] for i in existing
@@ -1600,7 +1599,7 @@ def adjust_substitutions(self, substitutions):
                     f"{self.get_location()}"
                     f"{existing_res}"
                 )
-            substitutions.insert(0, (self.name, value_repl))
+            substitutions.insert(0, (self.name, self.value))
             return
         if len(existing) > 1:
             raise ValueError(
@@ -1622,7 +1621,7 @@ def adjust_substitutions(self, substitutions):
                 f"Expected pattern: {self.name}"
                 f"{existing_res}"
             )
-        substitutions[existing[0]] = (self.name, value_repl)
+        substitutions[existing[0]] = (self.name, self.value)
 
 
 def applySubstitutions(script, substitutions, conditions={}, recursion_limit=None):
@@ -1738,8 +1737,7 @@ def processLine(ln):
         # Apply substitutions
         ln = substituteIfElse(escapePercents(ln))
         for a, b in substitutions:
-            if kIsWindows:
-                b = b.replace("\\", "\\\\")
+            b = b.replace("\\", "\\\\")
             # re.compile() has a built-in LRU cache with 512 entries. In some
             # test suites lit ends up thrashing that cache, which made e.g.
             # check-llvm run 50% slower.  Use an explicit, unbounded cache
diff --git a/llvm/utils/lit/tests/Inputs/shtest-define/lit.cfg b/llvm/utils/lit/tests/Inputs/shtest-define/lit.cfg
index a29755eb2b600..ffe7cce8f0336 100644
--- a/llvm/utils/lit/tests/Inputs/shtest-define/lit.cfg
+++ b/llvm/utils/lit/tests/Inputs/shtest-define/lit.cfg
@@ -23,6 +23,10 @@ config.substitutions.insert(
     0, ("%{global:echo}", "echo GLOBAL: %{global:greeting} %{global:what}")
 )
 
+# This substitution includes an re.sub replacement string escape sequence,
+# which lit should treat as plain text.
+config.substitutions.insert(0, ("%{global:subst-with-escapes}", r"value-with-\g"))
+
 # The following substitution definitions are confusing and should be avoided.
 # We define them here so we can test that 'DEFINE:' and 'REDEFINE:' directives
 # guard against the confusion they cause.
diff --git a/llvm/utils/lit/tests/Inputs/shtest-define/value-escaped.txt b/llvm/utils/lit/tests/Inputs/shtest-define/value-escaped.txt
index 68cf35825e2a6..92fe4c27664fa 100644
--- a/llvm/utils/lit/tests/Inputs/shtest-define/value-escaped.txt
+++ b/llvm/utils/lit/tests/Inputs/shtest-define/value-escaped.txt
@@ -1,16 +1,16 @@
-# FIXME: The doubled backslashes occur under windows.  That's almost surely a
-# lit issue beyond DEFINE/REDEFINE.
-
 # Escape sequences that can appear in python re.sub replacement strings have no
 # special meaning in the value.
 
 # DEFINE: %{escape} = \g<0>\n
 # RUN: echo '%{escape}'
-# CHECK:# | {{\\?}}\g<0>{{\\?}}\n
+# CHECK:# | \g<0>\n
 
 # REDEFINE: %{escape} = \n                                                     \
 # REDEFINE:             \g<param>
 # RUN: echo '%{escape}'
-# CHECK:# | {{\\?}}\n {{\\?}}\g<param>
+# CHECK:# | \n \g<param>
+
+# RUN: echo '%{global:subst-with-escapes}'
+# CHECK:# | value-with-\g
 
 # CHECK: Passed: 1 {{\([0-9]*.[0-9]*%\)}}