diff --git a/changelog/9791.bugfix.rst b/changelog/9791.bugfix.rst
new file mode 100644
index 00000000000..f81c870165b
--- /dev/null
+++ b/changelog/9791.bugfix.rst
@@ -0,0 +1 @@
+Fixed a path handling code in ``rewrite.py`` that seems to work fine, but was incorrect and fails in some systems.
diff --git a/src/_pytest/assertion/rewrite.py b/src/_pytest/assertion/rewrite.py
index 81096764e04..7a55ff0eeed 100644
--- a/src/_pytest/assertion/rewrite.py
+++ b/src/_pytest/assertion/rewrite.py
@@ -190,7 +190,7 @@ def _early_rewrite_bailout(self, name: str, state: "AssertionState") -> bool:
             return False
 
         # For matching the name it must be as if it was a filename.
-        path = PurePath(os.path.sep.join(parts) + ".py")
+        path = PurePath(os.path.join(*parts) + ".py")
 
         for pat in self.fnpats:
             # if the pattern contains subdirectories ("tests/**.py" for example) we can't bail out based