diff --git a/.eslintrc b/.eslintrc
index 459b3d4..c137b67 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -5,9 +5,9 @@
 		"complexity": 0,
 		"func-style": [2, 'declaration'],
         "indent": [2, 4],
-        "max-lines-per-function": [2, 120],
+        "max-lines-per-function": [2, 130],
         "max-params": [2, 4],
-		"max-statements": [2, 80],
+		"max-statements": [2, 90],
         "max-statements-per-line": [2, { "max": 2 }],
         "no-magic-numbers": 0,
 		"no-param-reassign": 1,
@@ -15,6 +15,8 @@
     },
     "globals": {
         "BigInt": false,
+        "WeakSet": false,
+        "WeakMap": false,
     },
     "overrides": [
         {
diff --git a/.nycrc b/.nycrc
index b65425a..7b95a1e 100644
--- a/.nycrc
+++ b/.nycrc
@@ -4,10 +4,10 @@
   "instrumentation": false,
   "sourceMap": false,
   "reporter": ["html", "text-summary"],
-  "lines": 94,
-  "statements": 94,
+  "lines": 93,
+  "statements": 93,
   "functions": 96,
-  "branches": 90,
+  "branches": 89,
   "exclude": [
     "coverage",
     "example",
diff --git a/index.js b/index.js
index 0cac810..1394e53 100644
--- a/index.js
+++ b/index.js
@@ -6,6 +6,10 @@ var hasSet = typeof Set === 'function' && Set.prototype;
 var setSizeDescriptor = Object.getOwnPropertyDescriptor && hasSet ? Object.getOwnPropertyDescriptor(Set.prototype, 'size') : null;
 var setSize = hasSet && setSizeDescriptor && typeof setSizeDescriptor.get === 'function' ? setSizeDescriptor.get : null;
 var setForEach = hasSet && Set.prototype.forEach;
+var hasWeakMap = typeof WeakMap === 'function' && WeakMap.prototype;
+var weakMapHas = hasWeakMap ? WeakMap.prototype.has : null;
+var hasWeakSet = typeof WeakSet === 'function' && WeakSet.prototype;
+var weakSetHas = hasWeakSet ? WeakSet.prototype.has : null;
 var booleanValueOf = Boolean.prototype.valueOf;
 var objectToString = Object.prototype.toString;
 var match = String.prototype.match;
@@ -113,6 +117,12 @@ module.exports = function inspect_(obj, options, depth, seen) {
         });
         return collectionOf('Set', setSize.call(obj), setParts);
     }
+    if (isWeakMap(obj)) {
+        return weakCollectionOf('WeakMap');
+    }
+    if (isWeakSet(obj)) {
+        return weakCollectionOf('WeakSet');
+    }
     if (isNumber(obj)) {
         return markBoxed(inspect(Number(obj)));
     }
@@ -192,6 +202,22 @@ function isMap(x) {
     return false;
 }
 
+function isWeakMap(x) {
+    if (!weakMapHas || !x || typeof x !== 'object') {
+        return false;
+    }
+    try {
+        weakMapHas.call(x, weakMapHas);
+        try {
+            weakSetHas.call(x, weakSetHas);
+        } catch (s) {
+            return true;
+        }
+        return x instanceof WeakMap; // core-js workaround, pre-v2.5.0
+    } catch (e) {}
+    return false;
+}
+
 function isSet(x) {
     if (!setSize || !x || typeof x !== 'object') {
         return false;
@@ -208,6 +234,22 @@ function isSet(x) {
     return false;
 }
 
+function isWeakSet(x) {
+    if (!weakSetHas || !x || typeof x !== 'object') {
+        return false;
+    }
+    try {
+        weakSetHas.call(x, weakSetHas);
+        try {
+            weakMapHas.call(x, weakMapHas);
+        } catch (s) {
+            return true;
+        }
+        return x instanceof WeakSet; // core-js workaround, pre-v2.5.0
+    } catch (e) {}
+    return false;
+}
+
 function isElement(x) {
     if (!x || typeof x !== 'object') { return false; }
     if (typeof HTMLElement !== 'undefined' && x instanceof HTMLElement) {
@@ -235,6 +277,10 @@ function markBoxed(str) {
     return 'Object(' + str + ')';
 }
 
+function weakCollectionOf(type) {
+    return type + ' { ? }';
+}
+
 function collectionOf(type, size, entries) {
     return type + ' (' + size + ') {' + entries.join(', ') + '}';
 }
diff --git a/test/values.js b/test/values.js
index 02b0f5b..20709d5 100644
--- a/test/values.js
+++ b/test/values.js
@@ -87,6 +87,16 @@ test('Map', { skip: typeof Map !== 'function' }, function (t) {
     t.end();
 });
 
+test('WeakMap', { skip: typeof WeakMap !== 'function' }, function (t) {
+    var map = new WeakMap();
+    map.set({ a: 1 }, ['b']);
+    var expectedString = 'WeakMap { ? }';
+    t.equal(inspect(map), expectedString, 'new WeakMap([[{ a: 1 }, ["b"]]]) should not show size or contents');
+    t.equal(inspect(new WeakMap()), 'WeakMap { ? }', 'empty WeakMap should not show as empty');
+
+    t.end();
+});
+
 test('Set', { skip: typeof Set !== 'function' }, function (t) {
     var set = new Set();
     set.add({ a: 1 });
@@ -103,6 +113,16 @@ test('Set', { skip: typeof Set !== 'function' }, function (t) {
     t.end();
 });
 
+test('WeakSet', { skip: typeof WeakSet !== 'function' }, function (t) {
+    var map = new WeakSet();
+    map.add({ a: 1 });
+    var expectedString = 'WeakSet { ? }';
+    t.equal(inspect(map), expectedString, 'new WeakSet([{ a: 1 }]) should not show size or contents');
+    t.equal(inspect(new WeakSet()), 'WeakSet { ? }', 'empty WeakSet should not show as empty');
+
+    t.end();
+});
+
 test('Strings', function (t) {
     var str = 'abc';