diff --git a/tests/test-extension.t b/tests/test-extension.t
--- a/tests/test-extension.t
+++ b/tests/test-extension.t
@@ -97,13 +97,13 @@
   $ cat > foo.py <<EOF
   > import os
   > name = os.path.basename(__file__).rsplit('.', 1)[0]
-  > print("1) %s imported" % name)
+  > print("1) %s imported" % name, flush=True)
   > def uisetup(ui):
-  >     print("2) %s uisetup" % name)
+  >     print("2) %s uisetup" % name, flush=True)
   > def extsetup():
-  >     print("3) %s extsetup" % name)
+  >     print("3) %s extsetup" % name, flush=True)
   > def reposetup(ui, repo):
-  >    print("4) %s reposetup" % name)
+  >    print("4) %s reposetup" % name, flush=True)
   > 
   > bytesname = name.encode('utf-8')
   > # custom predicate to check registration of functions at loading
@@ -195,7 +195,7 @@
   $ cat > loadabs.py <<EOF
   > import mod.ambigabs as ambigabs
   > def extsetup():
-  >     print('ambigabs.s=%s' % ambigabs.s)
+  >     print('ambigabs.s=%s' % ambigabs.s, flush=True)
   > EOF
   $ (PYTHONPATH=${PYTHONPATH}${PATHSEP}${TESTTMP}/libroot; hg --config extensions.loadabs=loadabs.py root)
   ambigabs.s=libroot/ambig.py
@@ -209,7 +209,7 @@
   $ cat > loadrel.py <<EOF
   > import mod.ambigrel as ambigrel
   > def extsetup():
-  >     print('ambigrel.s=%s' % ambigrel.s)
+  >     print('ambigrel.s=%s' % ambigrel.s, flush=True)
   > EOF
   $ (PYTHONPATH=${PYTHONPATH}${PATHSEP}${TESTTMP}/libroot; hg --config extensions.loadrel=loadrel.py root)
   ambigrel.s=libroot/mod/ambig.py
@@ -1744,7 +1744,7 @@
   > command = registrar.command(cmdtable)
   > @command(b'dummy', [(b'', b'opt', u'value', u'help')], 'ext [OPTIONS]')
   > def ext(*args, **opts):
-  >     print(opts[b'opt'])
+  >     print(opts[b'opt'], flush=True)
   > EOF
   $ cat > $TESTTMP/opt-unicode-default/.hg/hgrc << EOF
   > [extensions]