diff --git a/demos/echo/client.py b/demos/echo/client.py
index ad5ad4f8..140c14dc 100644
--- a/demos/echo/client.py
+++ b/demos/echo/client.py
@@ -35,7 +35,7 @@ def echo_forever(main_queue, main_event):
     except Exception:
         import traceback
         traceback.print_exc()
-        print("EXCEPT ('{}', {}) with fd {} over {}s".format(addr, port, fileno, cdelta + delta))
+        print("EXCEPT ('{0}', {1}) with fd {2} over {3}s".format(addr, port, fileno, cdelta + delta))
     finally:
         main_queue.put(_max)
 
@@ -57,7 +57,7 @@ def main():
             eid_proc[eid] = proc
         while True:
             alive = len([_proc for _proc in eid_proc.values() if _proc.is_alive()])
-            print('{}/{} alive'.format(alive, limit))
+            print('{0}/{1} alive'.format(alive, limit))
             if alive == 0:
                 print('All of the client processes are dead. Exiting loop...')
                 break
@@ -82,8 +82,8 @@ def main():
         else:
             delta = "unknown"
         time.sleep(1)
-        print("Max time to establish: {}".format(cdelta))
-        print("Max time   echo reply: {}".format(delta))
+        print("Max time to establish: {0}".format(cdelta))
+        print("Max time   echo reply: {0}".format(delta))
         print(cdelta, delta)
 
 
diff --git a/rpyc/core/vinegar.py b/rpyc/core/vinegar.py
index b182f807..c79425bb 100644
--- a/rpyc/core/vinegar.py
+++ b/rpyc/core/vinegar.py
@@ -27,7 +27,7 @@
 
 REMOTE_LINE_START = "\n\n========= Remote Traceback "
 REMOTE_LINE_END = " =========\n"
-REMOTE_LINE = "{}({{}}){}".format(REMOTE_LINE_START, REMOTE_LINE_END)
+REMOTE_LINE = "{0}({{}}){1}".format(REMOTE_LINE_START, REMOTE_LINE_END)
 
 
 try:
diff --git a/rpyc/lib/__init__.py b/rpyc/lib/__init__.py
index 50a30d9e..03c300cc 100644
--- a/rpyc/lib/__init__.py
+++ b/rpyc/lib/__init__.py
@@ -153,10 +153,10 @@ def exp_backoff(collision):
 def get_id_pack(obj):
     """introspects the given (local) object, returns id_pack as expected by BaseNetref"""
     if not inspect.isclass(obj):
-        name_pack = '{}.{}'.format(obj.__class__.__module__, obj.__class__.__name__)
+        name_pack = '{0}.{1}'.format(obj.__class__.__module__, obj.__class__.__name__)
         return (name_pack, id(type(obj)), id(obj))
     else:
-        name_pack = '{}.{}'.format(obj.__module__, obj.__name__)
+        name_pack = '{0}.{1}'.format(obj.__module__, obj.__name__)
         return (name_pack, id(obj), 0)