diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index a34eb29..6b9bb6b 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -698,7 +698,7 @@
                            errread, errwrite):
             """Execute program (MS Windows version)"""
 
-            if not isinstance(args, basestring):
+            if not isinstance(args, str):
                 args = list2cmdline(args)
 
             # Process startup details
@@ -913,7 +913,7 @@
                            errread, errwrite):
             """Execute program (POSIX version)"""
 
-            if isinstance(args, basestring):
+            if isinstance(args, str):
                 args = [args]
             else:
                 args = list(args)