diff --git a/types/convict/convict-tests.ts b/types/convict/convict-tests.ts
index 3bc0b4565f..daa07c6875 100644
--- a/types/convict/convict-tests.ts
+++ b/types/convict/convict-tests.ts
@@ -1,48 +1,41 @@
-
-/// <reference types="validator" />
-
 import convict = require('convict');
 import validator = require('validator');
 
 // define a schema
 
 // straight from the convict tests
-const format : convict.Format = {
+const format: convict.Format = {
   name: 'float-percent',
-  validate: function(val) {
+  validate(val) {
     if (val !== 0 && (!val || val > 1 || val < 0)) {
       throw new Error('must be a float between 0 and 1, inclusive');
     }
   },
-  coerce: function(val) {
-    return +(<string> val);
+  coerce(val) {
+    return parseFloat(val);
   }
 };
 
-
-
-
 convict.addFormat(format);
 convict.addFormats({
-      prime: {
-        validate: function(val) {
-          function isPrime(n: number) {
-            if (n <= 1) return false; // zero and one are not prime
-            for (var i=2; i*i <= n; i++) {
-              if (n % i === 0) return false;
-            }
-            return true;
-          }
-          if (!isPrime(val)) throw new Error('must be a prime number');
-        },
-        coerce: function(val) {
-          return parseInt(val, 10);
+  prime: {
+    validate(val) {
+      function isPrime(n: number) {
+        if (n <= 1) return false; // zero and one are not prime
+        for (let i = 2; i * i <= n; i++) {
+          if (n % i === 0) return false;
         }
+        return true;
       }
-    });
+      if (!isPrime(val)) throw new Error('must be a prime number');
+    },
+    coerce(val) {
+      return parseInt(val, 10);
+    }
+  }
+});
 
-
-var conf = convict({
+let conf = convict({
   env: {
     doc: 'The applicaton environment.',
     format: ['production', 'development', 'test'],
@@ -65,7 +58,11 @@ var conf = convict({
   },
   key: {
     doc: "API key",
-    format: (val: string) => validator.isUUID(val),
+    format: (val: string) => {
+      if (!validator.isUUID(val)) {
+        throw new Error('must be a valid UUID');
+      }
+    },
     default: '01527E56-8431-11E4-AF91-47B661C210CA'
   },
   db: {
@@ -81,7 +78,13 @@ var conf = convict({
       default: 0,
       env: 'PORT',
       arg: 'port',
-    }
+    },
+    password: {
+      doc: 'The database password.',
+      default: 'secret',
+      format: String,
+      sensitive: true,
+    },
   },
   primeNumber: {
     format: 'prime',
@@ -91,14 +94,12 @@ var conf = convict({
     format: 'float-percent',
     default: 0.5
   },
-
 });
 
-
 // load environment dependent configuration
 
-var env = conf.get('env');
-var dbip = conf.get('db.ip');
+let env = conf.get('env');
+let dbip = conf.get('db.ip');
 conf.loadFile('./config/' + env + '.json');
 conf.loadFile(['./configs/always.json', './configs/sometimes.json']);
 
@@ -118,7 +119,7 @@ conf
   .validate({ allowed: 'warn' })
   .toString();
 
-var port: number = conf.default('port');
+let port: number = conf.default('port');
 
 if (conf.has('key')) {
   conf.set('the.awesome', true);
diff --git a/types/convict/index.d.ts b/types/convict/index.d.ts
index 82b22ba2db..183d91ed91 100644
--- a/types/convict/index.d.ts
+++ b/types/convict/index.d.ts
@@ -1,11 +1,11 @@
-// Type definitions for convict 3.0
+// Type definitions for convict 4.0
 // Project: https://github.com/mozilla/node-convict
-// Definitions by: Wim Looman <https://github.com/Nemo157>, Vesa Poikajärvi <https://github.com/vesse>
+// Definitions by: Wim Looman <https://github.com/Nemo157>
+//                 Vesa Poikajärvi <https://github.com/vesse>
+//                 Eli Young <https://github.com/elyscape>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
-
 declare namespace convict {
-
     type ValidationMethod = 'strict' | 'warn';
 
     interface ValidateOptions {
@@ -23,8 +23,8 @@ declare namespace convict {
 
     interface Format {
         name?: string;
-        validate?: (val: any) => void;
-        coerce?: (val: any) => any;
+        validate?(val: any): void;
+        coerce?(val: any): any;
     }
 
     interface Schema {
@@ -35,16 +35,18 @@ declare namespace convict {
              * From the implementation:
              *
              *  format can be a:
-             *   - predefine type, as seen below
+             *   - predefined type, as seen below
              *   - an array of enumerated values, e.g. ["production", "development", "testing"]
              *   - built-in JavaScript type, i.e. Object, Array, String, Number, Boolean
-             *   - or if omitted, the Object.prototype.toString.call of the default value
+             *   - function that performs validation and throws an Error on failure
              *
-             * The docs also state that any function that validates is ok too
+             * If omitted, format will be set to the value of Object.prototype.toString.call
+             * for the default value
              */
-            format?: string | Array<any> | Function;
+            format?: string | any[] | ((val: any) => void);
             env?: string;
             arg?: string;
+            sensitive?: boolean;
         };
     }
 
@@ -78,17 +80,11 @@ declare namespace convict {
          */
         load(conf: Object): Config;
         /**
-         * Loads and merges one JSON configuration file into config
+         * Loads and merges JSON configuration file(s) into config
          *
          * @return {Config} instance
          */
-        loadFile(file: string): Config;
-        /**
-         * Loads and merges multiple JSON configuration files into config
-         *
-         * @return {Config} instance
-         */
-        loadFile(files: string[]): Config;
+        loadFile(files: string | string[]): Config;
         /**
          * Validates config against the schema used to initialize it
          *
diff --git a/types/convict/tslint.json b/types/convict/tslint.json
new file mode 100644
index 0000000000..09f94cd344
--- /dev/null
+++ b/types/convict/tslint.json
@@ -0,0 +1,7 @@
+{
+  "extends": "dtslint/dt.json",
+  "rules": {
+    // ban-types needs to be disabled to support TypeScript <2.2
+    "ban-types": false
+  }
+}