2 files changed, 47 insertions, 8 deletions

diff --git a/src/tox/config/loader/ini/replace.py b/src/tox/config/loader/ini/replace.py
index 40730ca5..41672780 100644
--- a/src/tox/config/loader/ini/replace.py
+++ b/src/tox/config/loader/ini/replace.py
@@ -30,7 +30,7 @@ LOGGER = logging.getLogger(__name__)
 ARG_DELIMITER = ":"
 REPLACE_START = "{"
 REPLACE_END = "}"
-BACKSLASH_ESCAPE_CHARS = ["\\", ARG_DELIMITER, REPLACE_START, REPLACE_END, "[", "]"]
+BACKSLASH_ESCAPE_CHARS = [ARG_DELIMITER, REPLACE_START, REPLACE_END, "[", "]"]
 MAX_REPLACE_DEPTH = 100
 
 
@@ -115,11 +115,18 @@ class MatchExpression:
         pos = 0
 
         while pos < len(value):
-            if len(value) > pos + 1 and value[pos] == "\\" and value[pos + 1] in BACKSLASH_ESCAPE_CHARS:
-                # backslash escapes the next character from a special set
-                last_arg.append(value[pos + 1])
-                pos += 2
-                continue
+            if len(value) > pos + 1 and value[pos] == "\\":
+                if value[pos + 1] in BACKSLASH_ESCAPE_CHARS:
+                    # backslash escapes the next character from a special set
+                    last_arg.append(value[pos + 1])
+                    pos += 2
+                    continue
+                if value[pos + 1] == "\\":
+                    # backlash doesn't escape a backslash, but does prevent it from affecting the next char
+                    # a subsequent `shlex` pass will eat the double backslash during command splitting
+                    last_arg.append(value[pos : pos + 2])
+                    pos += 2
+                    continue
             fragment = value[pos:]
             if terminator and fragment.startswith(terminator):
                 pos += len(terminator)
diff --git a/src/tox/config/loader/str_convert.py b/src/tox/config/loader/str_convert.py
index f07545f5..ad7ffa5d 100644
--- a/src/tox/config/loader/str_convert.py
+++ b/src/tox/config/loader/str_convert.py
@@ -46,10 +46,42 @@ class StrConvert(Convert[str]):
                     raise TypeError(f"dictionary lines must be of form key=value, found {row!r}")
 
     @staticmethod
+    def _win32_process_path_backslash(value: str, escape: str, special_chars: str) -> str:
+        """
+        Escape backslash in value that is not followed by a special character.
+
+        This allows windows paths to be written without double backslash, while
+        retaining the POSIX backslash escape semantics for quotes and escapes.
+        """
+        result = []
+        for ix, char in enumerate(value):
+            result.append(char)
+            if char == escape:
+                last_char = value[ix - 1 : ix]
+                if last_char == escape:
+                    continue
+                next_char = value[ix + 1 : ix + 2]
+                if next_char not in (escape, *special_chars):
+                    result.append(escape)  # escape escapes that are not themselves escaping a special character
+        return "".join(result)
+
+    @staticmethod
     def to_command(value: str) -> Command:
-        is_win = sys.platform == "win32"
+        """
+        At this point, ``value`` has already been substituted out, and all punctuation / escapes are final.
+
+        Value will typically be stripped of whitespace when coming from an ini file.
+        """
         value = value.replace(r"\#", "#")
-        splitter = shlex.shlex(value, posix=not is_win)
+        is_win = sys.platform == "win32"
+        if is_win:  # pragma: win32 cover
+            s = shlex.shlex(posix=True)
+            value = StrConvert._win32_process_path_backslash(
+                value,
+                escape=s.escape,
+                special_chars=s.quotes + s.whitespace,
+            )
+        splitter = shlex.shlex(value, posix=True)
         splitter.whitespace_split = True
         splitter.commenters = ""  # comments handled earlier, and the shlex does not know escaped comment characters
         args: list[str] = []