diff --git a/CONTRIBUTORS b/CONTRIBUTORS
index a95197ffb..39d848b4f 100644
--- a/CONTRIBUTORS
+++ b/CONTRIBUTORS
@@ -8,6 +8,7 @@ Anthon van der Neuth
 Anthony Sottile
 Ashley Whetter
 Asmund Grammeltwedt
+Barney Gale
 Barry Warsaw
 Bartolome Sanchez Salado
 Benoit Pierre
diff --git a/docs/changelog/1336.bugfix.rst b/docs/changelog/1336.bugfix.rst
new file mode 100644
index 000000000..17f9dd556
--- /dev/null
+++ b/docs/changelog/1336.bugfix.rst
@@ -0,0 +1,2 @@
+tox used Windows shell rules on non-Windows platforms when transforming
+positional arguments to a string - by :user:`barneygale`.
diff --git a/src/tox/config/__init__.py b/src/tox/config/__init__.py
index 19820d033..4437268e3 100644
--- a/src/tox/config/__init__.py
+++ b/src/tox/config/__init__.py
@@ -39,6 +39,12 @@
 from .parallel import add_parallel_config, add_parallel_flags
 from .reporter import add_verbosity_commands
 
+try:
+    from shlex import quote as shlex_quote
+except ImportError:
+    from pipes import quote as shlex_quote
+
+
 hookimpl = tox.hookimpl
 """DEPRECATED - REMOVE - this is left for compatibility with plugins importing this from here.
 
@@ -1674,7 +1680,10 @@ def getargvlist(cls, reader, value, replace=True):
     @classmethod
     def processcommand(cls, reader, command, replace=True):
         posargs = getattr(reader, "posargs", "")
-        posargs_string = list2cmdline([x for x in posargs if x])
+        if sys.platform.startswith("win"):
+            posargs_string = list2cmdline([x for x in posargs if x])
+        else:
+            posargs_string = " ".join([shlex_quote(x) for x in posargs if x])
 
         # Iterate through each word of the command substituting as
         # appropriate to construct the new command string. This
diff --git a/tests/unit/config/test_config.py b/tests/unit/config/test_config.py
index 7c1fa6045..2f019b791 100644
--- a/tests/unit/config/test_config.py
+++ b/tests/unit/config/test_config.py
@@ -730,8 +730,18 @@ def test_argvlist_posargs_with_quotes(self, newconfig):
                 cmd1 -f {posargs}
         """
         )
+        # The operating system APIs for launching processes differ between
+        # Windows and other OSs. On Windows, the command line is passed as a
+        # string (and not a list of strings). Python uses the MS C runtime
+        # rules for splitting this string into `sys.argv`, and those rules
+        # differ from POSIX shell rules in their treatment of quoted arguments.
+        if sys.platform.startswith("win"):
+            substitutions = ["foo", "'bar", "baz'"]
+        else:
+            substitutions = ["foo", "bar baz"]
+
         reader = SectionReader("section", config._cfg)
-        reader.addsubstitutions(["foo", "'bar", "baz'"])
+        reader.addsubstitutions(substitutions)
         assert reader.getargvlist("key1") == []
         x = reader.getargvlist("key2")
         assert x == [["cmd1", "-f", "foo", "bar baz"]]