--- hosts_access.c.orig
+++ hosts_access.c
@@ -354,7 +354,26 @@ char   *string;
 	/* If prefix was given, handle it */
 	if ((mask = split_at(token, '/')) != 0)
 	{
-		if (sscanf(mask, "%d", &prefixlen) != 1 || prefixlen < 0)
+		if (strchr(mask, '.') != NULL) /* We have something
+                                                  like 255.255.0.0  */
+                {
+		   int b1, b2, b3, b4;
+		   uint32_t netmask;
+
+		   if (sscanf(mask, "%d.%d.%d.%d", &b1, &b2, &b3, &b4) != 4)
+		   {
+			tcpd_warn ("Wrong netmask in %s", tok);
+			return (NO);
+		   }
+		   netmask = (((((b1 * 256) + b2) * 256) + b3) * 256) + b4;
+		   prefixlen = 0;
+		   while (netmask > 0)
+		   {
+			++prefixlen;
+			netmask  <<= 1;
+                   }
+                }
+		else if (sscanf(mask, "%d", &prefixlen) != 1 || prefixlen < 0)
 		{
 			tcpd_warn ("Wrong prefix length in %s", tok);
 			return (NO);