diff --git a/_pytest/config.py b/_pytest/config.py
index 68d66ee2a..c84bbe134 100644
--- a/_pytest/config.py
+++ b/_pytest/config.py
@@ -1327,14 +1327,15 @@ def determine_setup(inifile, args, warnfunc=None):
     dirs = get_dirs_from_args(args)
     if inifile:
         iniconfig = py.iniconfig.IniConfig(inifile)
-        is_cfg_file = '.cfg' in inifile
+        is_cfg_file = str(inifile).endswith('.cfg')
+        # TODO: [pytest] section in *.cfg files is depricated. Need refactoring.
         sections = ['tool:pytest', 'pytest'] if is_cfg_file else ['pytest']
         for section in sections:
             try:
                 inicfg = iniconfig[section]
                 if is_cfg_file and section == 'pytest' and warnfunc:
                     from _pytest.deprecated import SETUP_CFG_PYTEST
-                    warnfunc('C1', SETUP_CFG_PYTEST.replace('setup.cfg', inifile))
+                    warnfunc('C1', SETUP_CFG_PYTEST.replace('setup.cfg', str(inifile)))
                 break
             except KeyError:
                 inicfg = None