diff --git a/tests/run-tests.py b/tests/run-tests.py
--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -3432,11 +3432,10 @@
             if self.options.list_tests:
                 result = runner.listtests(suite)
             else:
+                self._usecorrectpython()
                 if self._installdir:
                     self._installhg()
                     self._checkhglib("Testing")
-                else:
-                    self._usecorrectpython()
                 if self.options.chg:
                     assert self._installdir
                     self._installchg()
@@ -3718,8 +3717,6 @@
             sys.exit(1)
         os.chdir(self._testdir)
 
-        self._usecorrectpython()
-
         hgbat = os.path.join(self._bindir, b'hg.bat')
         if os.path.isfile(hgbat):
             # hg.bat expects to be put in bin/scripts while run-tests.py