diff --git a/src/_pytest/fixtures.py b/src/_pytest/fixtures.py
index 46b201184..51c573575 100644
--- a/src/_pytest/fixtures.py
+++ b/src/_pytest/fixtures.py
@@ -1483,27 +1483,27 @@ class FixtureManager:
 
         return FuncFixtureInfo(argnames, initialnames, names_closure, arg2fixturedefs)
 
-    def pytest_plugin_registered(self, plugin: _PluggyPlugin) -> None:
-        nodeid = None
-        plugin_name = self.config.pluginmanager.get_name(plugin)
-
-        # Construct the base nodeid which is later used to check
-        # what fixtures are visible for particular tests (as denoted
-        # by their test id).
+    def pytest_plugin_registered(self, plugin: _PluggyPlugin, plugin_name: str) -> None:
+        # Fixtures defined in conftest plugins are only visible to within the
+        # conftest's directory. This is unlike fixtures in non-conftest plugins
+        # which have global visibility. So for conftests, construct the base
+        # nodeid from the plugin name (which is the conftest path).
         if plugin_name and plugin_name.endswith("conftest.py"):
-            # The plugin name is assumed to be equal to plugin.__file__
-            # for conftest plugins. The difference is that plugin_name
-            # has the correct capitalization on capital-insensitive
-            # systems (Windows).
-            p = absolutepath(plugin_name)
+            # Note: we explicitly do *not* use `plugin.__file__` here -- The
+            # difference is that plugin_name has the correct capitalization on
+            # case-insensitive systems (Windows) and other normalization issues
+            # (issue #11816).
+            conftestpath = absolutepath(plugin_name)
             try:
-                nodeid = str(p.parent.relative_to(self.config.rootpath))
+                nodeid = str(conftestpath.parent.relative_to(self.config.rootpath))
             except ValueError:
                 nodeid = ""
             if nodeid == ".":
                 nodeid = ""
             if os.sep != nodes.SEP:
                 nodeid = nodeid.replace(os.sep, nodes.SEP)
+        else:
+            nodeid = None
 
         self.parsefactories(plugin, nodeid)