--- a/tests/run-tests
+++ b/tests/run-tests
@@ -69,7 +69,7 @@ export TESTDIR
 INST="$HGTMP/install"
 PYTHONDIR="$INST/lib/python"
 cd ..
-if ${PYTHON-python} setup.py install --home="$INST" \
+if ${PYTHON-python} setup.py clean --all install --force --home="$INST" \
   --install-lib="$PYTHONDIR" > tests/install.err 2>&1
 then
     rm tests/install.err

--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -69,8 +69,9 @@ def install_hg():
     installerrs = os.path.join("tests", "install.err")
 
     os.chdir("..") # Get back to hg root
-    cmd = '%s setup.py install --home="%s" --install-lib="%s" >%s 2>&1' % \
-        (sys.executable, INST, PYTHONDIR, installerrs)
+    cmd = ('%s setup.py clean --all'
+           ' install --force --home="%s" --install-lib="%s" >%s 2>&1'
+           % (sys.executable, INST, PYTHONDIR, installerrs))
     vlog("# Running", cmd)
     if os.system(cmd) == 0:
         if not verbose: