diff --git a/src/enum_net.cpp b/src/enum_net.cpp
index fe9d99192..72e7481e9 100644
--- a/src/enum_net.cpp
+++ b/src/enum_net.cpp
@@ -699,10 +699,30 @@ int _System __libsocket_sysctl(int* mib, u_int namelen, void *oldp, size_t *oldl
 				for (IP_ADAPTER_UNICAST_ADDRESS* unicast = adapter->FirstUnicastAddress;
 					unicast; unicast = unicast->Next)
 				{
-					if (!valid_addr_family(unicast->Address.lpSockaddr->sa_family))
+					auto const family = unicast->Address.lpSockaddr->sa_family;
+					if (!valid_addr_family(family))
 						continue;
 					r.preferred = unicast->DadState == IpDadStatePreferred;
 					r.interface_address = sockaddr_to_address(unicast->Address.lpSockaddr);
+					// OnLinkPrefixLength is only present on Vista and newer
+					int const max_prefix_len = family == AF_INET ? 32 : 128;
+					if (unicast->Length >= 64 && unicast->OnLinkPrefixLength <= max_prefix_len)
+					{
+						r.netmask = build_netmask(unicast->OnLinkPrefixLength, family);
+					}
+
+					if (family == AF_INET6 && (unicast->PrefixOrigin == IpPrefixOriginDhcp
+						|| unicast->SuffixOrigin == IpSuffixOriginRandom))
+					{
+						// DHCPv6 does not specify a subnet mask (it should be taken from the RA)
+						// but apparently MS didn't get the memo and incorrectly reports a
+						// prefix length of 128 for DHCPv6 assigned addresses
+						// 128 is also reported for privacy addresses despite claiming to
+						// have gotten the prifix length from the RA *shrug*
+						// use a 64 bit prefix in these cases since that is likely to be
+						// the correct value, or at least less wrong than 128
+						r.netmask = build_netmask(64, family);
+					}
 					ret.push_back(r);
 				}
 			}