diff --git a/src/cowrie/commands/nc.py b/src/cowrie/commands/nc.py
index c47111b7..a6048894 100644
--- a/src/cowrie/commands/nc.py
+++ b/src/cowrie/commands/nc.py
@@ -25,6 +25,7 @@ def makeMask(n):
 def dottedQuadToNum(ip):
     """
     convert decimal dotted quad string to long integer
+    this will throw builtins.OSError on failure
     """
     return struct.unpack('I', socket.inet_aton(ip))[0]
 
@@ -72,7 +73,7 @@ usage: nc [-46bCDdhjklnrStUuvZz] [-I length] [-i interval] [-O length]
         host = args[0]
         port = args[1]
 
-        if not re.match(r'\d+', port):
+        if not re.match(r'^\d+$', port):
             self.errorWrite('nc: port number invalid: {}\n'.format(port))
             self.exit()
             return
@@ -80,10 +81,15 @@ usage: nc [-46bCDdhjklnrStUuvZz] [-I length] [-i interval] [-O length]
         if re.match(r'^\d+$', host):
             address = int(host)
         elif re.match(r'^[\d\.]+$', host):
-            address = dottedQuadToNum(host)
+            try:
+                address = dottedQuadToNum(host)
+            except OSError:
+                self.exit()
+                return
         else:
             # TODO: should do dns lookup
             self.exit()
+            return
 
         for net in local_networks:
             if addressInNetwork(address, net):