diff --git a/pym/utils/ip.py b/pym/utils/ip.py
index a1ec1be..2ec2852 100644
--- a/pym/utils/ip.py
+++ b/pym/utils/ip.py
@@ -48,7 +48,7 @@ IP_ADDR_NET = "(%(ipaddr)s)/((%(ipnet)s))"%{'ipaddr':IP_NET,
 reIp = re.compile("^{0}$".format(IP_ADDR))
 reNetSuffix = re.compile("^{0}$".format(IP_NET_SUFFIX))
 reNet = re.compile("^{0}$".format(IP_ADDR_NET))
-reMask = re.compile("^{}$".format(IP_MASK))
+reMask = re.compile("^{0}$".format(IP_MASK))
 
 def checkIp(ip):
     """Check ip"""