diff --git a/examples/mk_simple_certs.py b/examples/mk_simple_certs.py
index 7a24a4f..84429f4 100644
--- a/examples/mk_simple_certs.py
+++ b/examples/mk_simple_certs.py
@@ -9,9 +9,11 @@
 cacert = createCertificate(careq, (careq, cakey), 0, (0, 60*60*24*365*5)) # five years
 
 print('Creating Certificate Authority private key in "simple/CA.pkey"')
-open('simple/CA.pkey', 'w').write(crypto.dump_privatekey(crypto.FILETYPE_PEM, cakey).decode('utf-8'))
+with open('simple/CA.pkey', 'w') as capkey:
+    capkey.write(crypto.dump_privatekey(crypto.FILETYPE_PEM, cakey).decode('utf-8'))
 print('Creating Certificate Authority certificate in "simple/CA.cert"')
-open('simple/CA.cert', 'w').write(crypto.dump_certificate(crypto.FILETYPE_PEM, cacert).decode('utf-8'))
+with open('simple/CA.cert', 'w') as ca:
+    ca.write(crypto.dump_certificate(crypto.FILETYPE_PEM, cacert).decode('utf-8'))
 
 for (fname, cname) in [('client', 'Simple Client'), ('server', 'Simple Server')]:
     pkey = createKeyPair(TYPE_RSA, 2048)
@@ -19,6 +21,9 @@
     cert = createCertificate(req, (cacert, cakey), 1, (0, 60*60*24*365*5)) # five years
 
     print('Creating Certificate %s private key in "simple/%s.pkey"' % (fname, fname))
-    open('simple/%s.pkey' % (fname,), 'w').write(crypto.dump_privatekey(crypto.FILETYPE_PEM, pkey).decode('utf-8'))
+    with open('simple/%s.pkey' % (fname,), 'w') as leafpkey:
+        leafpkey.write(crypto.dump_privatekey(crypto.FILETYPE_PEM, pkey).decode('utf-8'))
     print('Creating Certificate %s certificate in "simple/%s.cert"' % (fname, fname))
-    open('simple/%s.cert' % (fname,), 'w').write(crypto.dump_certificate(crypto.FILETYPE_PEM, cert).decode('utf-8'))
+    with open('simple/%s.cert' % (fname,), 'w') as leafcert:
+        leafcert.write(crypto.dump_certificate(crypto.FILETYPE_PEM, cert).decode('utf-8'))
+