diff --git a/CHANGES b/CHANGES
index 8fa86a98b26..fe9e8e28bca 100644
--- a/CHANGES
+++ b/CHANGES
@@ -13,6 +13,8 @@ Deprecated
 Features added
 --------------
 
+* #8959: using UNIX path separator in image directive confuses Sphinx on Windows
+
 Bugs fixed
 ----------
 
diff --git a/sphinx/environment/__init__.py b/sphinx/environment/__init__.py
index af3e2b8d542..20e76d826e6 100644
--- a/sphinx/environment/__init__.py
+++ b/sphinx/environment/__init__.py
@@ -10,7 +10,6 @@
 
 import os
 import pickle
-import posixpath
 import warnings
 from collections import defaultdict
 from copy import copy
@@ -358,7 +357,7 @@ def relfn2path(self, filename: str, docname: str = None) -> Tuple[str, str]:
                                                 base=None))
             rel_fn = path.join(docdir, filename)
 
-        return (posixpath.normpath(rel_fn),
+        return (path.normpath(rel_fn),
                 path.normpath(path.join(self.srcdir, rel_fn)))
 
     @property