diff --git a/include/uv.h b/include/uv.h
index a6688131..3b61e28f 100644
--- a/include/uv.h
+++ b/include/uv.h
@@ -1479,6 +1479,10 @@ struct uv_interface_address_s {
     struct sockaddr_in address4;
     struct sockaddr_in6 address6;
   } address;
+  union {
+    struct sockaddr_in netmask4;
+    struct sockaddr_in6 netmask6;
+  } netmask;
 };
 
 UV_EXTERN char** uv_setup_args(int argc, char** argv);
diff --git a/src/unix/aix.c b/src/unix/aix.c
index 5ea33bbc..e1f247a7 100644
--- a/src/unix/aix.c
+++ b/src/unix/aix.c
@@ -369,6 +369,8 @@ uv_err_t uv_interface_addresses(uv_interface_address_t** addresses,
       address->address.address4 = *((struct sockaddr_in *)&p->ifr_addr);
     }
 
+    /* TODO: Retrieve netmask using SIOCGIFNETMASK ioctl */
+
     address->is_internal = flg.ifr_flags & IFF_LOOPBACK ? 1 : 0;
 
     address++;
diff --git a/src/unix/darwin.c b/src/unix/darwin.c
index 85a1d9ad..e641b500 100644
--- a/src/unix/darwin.c
+++ b/src/unix/darwin.c
@@ -408,6 +408,12 @@ uv_err_t uv_interface_addresses(uv_interface_address_t** addresses,
       address->address.address4 = *((struct sockaddr_in *)ent->ifa_addr);
     }
 
+    if (ent->ifa_netmask->sa_family == AF_INET6) {
+      address->netmask.netmask6 = *((struct sockaddr_in6 *)ent->ifa_netmask);
+    } else {
+      address->netmask.netmask4 = *((struct sockaddr_in *)ent->ifa_netmask);
+    }
+
     address->is_internal = ent->ifa_flags & IFF_LOOPBACK ? 1 : 0;
 
     address++;
diff --git a/src/unix/linux-core.c b/src/unix/linux-core.c
index 23a59772..13ed0c5e 100644
--- a/src/unix/linux-core.c
+++ b/src/unix/linux-core.c
@@ -693,6 +693,12 @@ uv_err_t uv_interface_addresses(uv_interface_address_t** addresses,
       address->address.address4 = *((struct sockaddr_in *)ent->ifa_addr);
     }
 
+    if (ent->ifa_netmask->sa_family == AF_INET6) {
+      address->netmask.netmask6 = *((struct sockaddr_in6 *)ent->ifa_netmask);
+    } else {
+      address->netmask.netmask4 = *((struct sockaddr_in *)ent->ifa_netmask);
+    }
+
     address->is_internal = ent->ifa_flags & IFF_LOOPBACK ? 1 : 0;
 
     address++;
diff --git a/src/unix/netbsd.c b/src/unix/netbsd.c
index 0fbcf108..9d3b2146 100644
--- a/src/unix/netbsd.c
+++ b/src/unix/netbsd.c
@@ -331,6 +331,12 @@ uv_err_t uv_interface_addresses(uv_interface_address_t** addresses, int* count)
       address->address.address4 = *((struct sockaddr_in *)ent->ifa_addr);
     }
 
+    if (ent->ifa_netmask->sa_family == AF_INET6) {
+      address->netmask.netmask6 = *((struct sockaddr_in6 *)ent->ifa_netmask);
+    } else {
+      address->netmask.netmask4 = *((struct sockaddr_in *)ent->ifa_netmask);
+    }
+
     address->is_internal = !!(ent->ifa_flags & IFF_LOOPBACK) ? 1 : 0;
 
     address++;
diff --git a/src/unix/sunos.c b/src/unix/sunos.c
index ff5044cf..1bec39c0 100644
--- a/src/unix/sunos.c
+++ b/src/unix/sunos.c
@@ -622,6 +622,12 @@ uv_err_t uv_interface_addresses(uv_interface_address_t** addresses,
       address->address.address4 = *((struct sockaddr_in *)ent->ifa_addr);
     }
 
+    if (ent->ifa_netmask->sa_family == AF_INET6) {
+      address->netmask.netmask6 = *((struct sockaddr_in6 *)ent->ifa_netmask);
+    } else {
+      address->netmask.netmask4 = *((struct sockaddr_in *)ent->ifa_netmask);
+    }
+
     address->is_internal = ent->ifa_flags & IFF_PRIVATE || ent->ifa_flags &
 	IFF_LOOPBACK ? 1 : 0;
 
diff --git a/src/win/util.c b/src/win/util.c
index 96b1abe5..be076814 100644
--- a/src/win/util.c
+++ b/src/win/util.c
@@ -31,6 +31,7 @@
 #include "uv.h"
 #include "internal.h"
 
+#include <Winsock2.h>
 #include <iphlpapi.h>
 #include <psapi.h>
 #include <tlhelp32.h>
@@ -765,7 +766,7 @@ uv_err_t uv_interface_addresses(uv_interface_address_t** addresses_ptr,
     /* ERROR_BUFFER_OVERFLOW, and the required buffer size will be stored in */
     /* win_address_buf_size. */
     r = GetAdaptersAddresses(AF_UNSPEC,
-                             0,
+                             GAA_FLAG_INCLUDE_PREFIX,
                              NULL,
                              win_address_buf,
                              &win_address_buf_size);
@@ -882,6 +883,7 @@ uv_err_t uv_interface_addresses(uv_interface_address_t** addresses_ptr,
        win_address != NULL;
        win_address = win_address->Next) {
     IP_ADAPTER_UNICAST_ADDRESS_XP* unicast_address;
+    IP_ADAPTER_PREFIX* prefix;
     int name_size;
     size_t max_name_size;
 
@@ -907,21 +909,55 @@ uv_err_t uv_interface_addresses(uv_interface_address_t** addresses_ptr,
       return uv__new_sys_error(GetLastError());
     }
 
+    prefix = win_address->FirstPrefix;
+
     /* Add an uv_interface_address_t element for every unicast address. */
     for (unicast_address = (IP_ADAPTER_UNICAST_ADDRESS_XP*)
                            win_address->FirstUnicastAddress;
          unicast_address != NULL;
          unicast_address = unicast_address->Next) {
       struct sockaddr* sa;
+      int prefixlen;
 
       uv_address->name = name_buf;
 
+      /* Walk the prefix list in sync with the address list and extract
+         the prefixlen for each address.  On Vista and newer, we could
+         instead just use: unicast_address->OnLinkPrefixLength */
+      if (prefix != NULL) {
+        prefixlen = prefix->PrefixLength;
+        prefix = prefix->Next;
+      } else {
+        prefixlen = 0;
+      }
+
       sa = unicast_address->Address.lpSockaddr;
-      if (sa->sa_family == AF_INET6)
+      if (sa->sa_family == AF_INET6) {
+        int i;
+
         uv_address->address.address6 = *((struct sockaddr_in6 *) sa);
-      else
+
+        uv_address->netmask.netmask6.sin6_family = AF_INET6;
+        prefixlen = prefixlen > 0 ? prefixlen : 128;
+        for (i = 0; i < 16; ++i) {
+          int bits;
+          uint8_t byte_val;
+
+          bits = prefixlen < 8 ? prefixlen : 8;
+          byte_val = ~(0xff >> bits);
+          prefixlen -= bits;
+
+          uv_address->netmask.netmask6.sin6_addr.s6_addr[i] = byte_val;
+        }
+      } else {
         uv_address->address.address4 = *((struct sockaddr_in *) sa);
 
+        uv_address->netmask.netmask4.sin_family = AF_INET;
+        prefixlen = prefixlen > 0 ? prefixlen : 32;
+        uv_address->netmask.netmask4.sin_addr.s_addr =
+          htonl(0xffffffff << (32 - prefixlen));
+      }
+
       uv_address->is_internal =
           (win_address->IfType == IF_TYPE_SOFTWARE_LOOPBACK);
 
diff --git a/test/test-platform-output.c b/test/test-platform-output.c
index 008d14fb..80737a78 100644
--- a/test/test-platform-output.c
+++ b/test/test-platform-output.c
@@ -80,6 +80,14 @@ TEST_IMPL(platform_output) {
     }
 
     printf("  address: %s\n", buffer);
+
+    if (interfaces[i].netmask.netmask4.sin_family == AF_INET) {
+      uv_ip4_name(&interfaces[i].netmask.netmask4, buffer, sizeof(buffer));
+    } else if (interfaces[i].netmask.netmask4.sin_family == AF_INET6) {
+      uv_ip6_name(&interfaces[i].netmask.netmask6, buffer, sizeof(buffer));
+    }
+
+    printf("  netmask: %s\n", buffer);
   }
   uv_free_interface_addresses(interfaces, count);