diff --git a/update-local-certificates b/update-local-certificates
index 1541d7d..97cf06e 100755
--- a/update-local-certificates
+++ b/update-local-certificates
@@ -10,5 +10,7 @@ security find-certificate -a -p /Library/Keychains/System.keychain > $tmp_certs
 security find-certificate -a -p /System/Library/Keychains/SystemRootCertificates.keychain >> $tmp_certs
 security find-certificate -a -p >> $tmp_certs
 
-chmod a+r $tmp_certs
-mv $tmp_certs $certs
+if [[ `md5 $tmp_certs | cut -d'=' -f2` != `md5 $certs | cut -d'=' -f2` ]]; then
+    chmod a+r $tmp_certs
+    mv $tmp_certs $certs
+fi