diff --git a/README.md b/README.md
index 6876a3b..f57725b 100644
--- a/README.md
+++ b/README.md
@@ -173,7 +173,7 @@ addr.octets // => [192, 168, 1, 1]
 ```
 
 `prefixLengthFromSubnetMask()` will return a CIDR prefix length for a valid IPv4 netmask or
-false if the netmask is not valid.
+null if the netmask is not valid.
 
 ```js
 ipaddr.IPv4.parse('255.255.255.240').prefixLengthFromSubnetMask() == 28
diff --git a/lib/ipaddr.js.d.ts b/lib/ipaddr.js.d.ts
index ef01ac4..52174b6 100644
--- a/lib/ipaddr.js.d.ts
+++ b/lib/ipaddr.js.d.ts
@@ -1,7 +1,4 @@
-
-
 declare module "ipaddr.js" {
-
     type IPv4Range = 'unicast' | 'unspecified' | 'broadcast' | 'multicast' | 'linkLocal' | 'loopback' | 'carrierGradeNat' | 'private' | 'reserved';
     type IPv6Range = 'unicast' | 'unspecified' | 'linkLocal' | 'multicast' | 'loopback' | 'uniqueLocal' | 'ipv4Mapped' | 'rfc6145' | 'rfc6052' | '6to4' | 'teredo' | 'reserved';
 
@@ -9,23 +6,20 @@ declare module "ipaddr.js" {
         [name: string]: [T, number] | [T, number][];
     }
 
-
     // Common methods/properties for IPv4 and IPv6 classes.
     class IP {
-
-        prefixLengthFromSubnetMask(): number | false;
+        prefixLengthFromSubnetMask(): number | null;
         toByteArray(): number[];
         toNormalizedString(): string;
         toString(): string;
     }
 
     namespace Address {
-
         export function isValid(addr: string): boolean;
         export function fromByteArray(bytes: number[]): IPv4 | IPv6;
         export function parse(addr: string): IPv4 | IPv6;
         export function parseCIDR(mask: string): [IPv4 | IPv6, number];
-        export function process(address: string): IPv4 | IPv6;
+        export function process(addr: string): IPv4 | IPv6;
         export function subnetMatch(addr: IPv4, rangeList: RangeList<IPv4>, defaultName?: string): string;
         export function subnetMatch(addr: IPv6, rangeList: RangeList<IPv6>, defaultName?: string): string;
 
@@ -39,6 +33,7 @@ declare module "ipaddr.js" {
             static parseCIDR(addr: string): [IPv4, number];
             static subnetMaskFromPrefixLength(prefix: number): IPv4;
             constructor(octets: number[]);
+            octets: number[]
 
             kind(): 'ipv4';
             match(addr: IPv4, bits: number): boolean;
@@ -55,7 +50,9 @@ declare module "ipaddr.js" {
             static parse(addr: string): IPv6;
             static parseCIDR(addr: string): [IPv6, number];
             static subnetMaskFromPrefixLength(prefix: number): IPv6;
-            constructor(octets: number[]);
+            constructor(parts: number[]);
+            parts: number[]
+            zoneId?: string
 
             isIPv4MappedAddress(): boolean;
             kind(): 'ipv6';
diff --git a/package.json b/package.json
index 7e092f1..1e07cce 100644
--- a/package.json
+++ b/package.json
@@ -9,8 +9,8 @@
   "dependencies": {},
   "devDependencies": {
     "coffee-script": "~1.12.6",
-    "uglify-js": "~3.0.19",
-    "nodeunit": ">=0.8.2 <0.8.7"
+    "nodeunit": "^0.11.3",
+    "uglify-js": "~3.0.19"
   },
   "scripts": {
     "test": "cake build test"