diff --git a/index.js b/index.js
index 190efbc..44fd605 100644
--- a/index.js
+++ b/index.js
@@ -2,6 +2,10 @@ var hasOwnProp = Object.prototype.hasOwnProperty;
 
 module.exports = deep;
 
+function isSafeKey (key) {
+  return key !== '__proto__' && key !== 'prototype' && key !== 'constructor';
+}
+
 function deep (obj, path, value) {
   if (arguments.length === 3) return set.apply(null, arguments);
   return get.apply(null, arguments);
@@ -11,7 +15,7 @@ function get (obj, path) {
   var keys = Array.isArray(path) ? path : path.split('.');
   for (var i = 0; i < keys.length; i++) {
     var key = keys[i];
-    if (!obj || !hasOwnProp.call(obj, key)) {
+    if (!obj || !hasOwnProp.call(obj, key) || !isSafeKey(key)) {
       obj = undefined;
       break;
     }
@@ -24,6 +28,7 @@ function set (obj, path, value) {
   var keys = Array.isArray(path) ? path : path.split('.');
   for (var i = 0; i < keys.length - 1; i++) {
     var key = keys[i];
+    if (!isSafeKey(key)) return;
     if (deep.p && !hasOwnProp.call(obj, key)) obj[key] = {};
     obj = obj[key];
   }
diff --git a/test.js b/test.js
index beecbf1..73603ec 100644
--- a/test.js
+++ b/test.js
@@ -98,3 +98,52 @@ test('deep deletes', function (t) {
   t.equal(deep(obj, 'bar.baz.beep'), undefined);
   t.end();
 });
+
+test('do not get `__proto__`, `prototype` or `constructor` properties', function (t) {
+  var obj = {
+    isAdmin: false,
+    __proto__: {
+      isAdmin: true
+    },
+    prototype: {
+      isAdmin: true
+    },
+    constructor: {
+      isAdmin: true,
+      prototype: {
+        isAdmin: true
+      }
+    }
+  };
+
+  t.equal(deep(obj, 'isAdmin'), false);
+  t.equal(deep(obj, '__proto__.isAdmin'), undefined);
+  t.equal(deep(obj, 'prototype.isAdmin'), undefined);
+  t.equal(deep(obj, 'constructor.isAdmin'), undefined);
+  t.equal(deep(obj, 'constructor.prototype.isAdmin'), undefined);
+  t.end();
+});
+
+test('do not set `__proto__`, `prototype` or `constructor` properties', function (t) {
+  var obj = {};
+
+  deep.p = true;
+
+  deep(obj, 'isAdmin', false);
+  deep(obj, '__proto__.isAdmin', true);
+  deep(obj, 'prototype.isAdmin', true);
+  deep(obj, 'constructor.isAdmin', true);
+  deep(obj, 'constructor.prototype.isAdmin', true);
+
+  t.equal(obj.isAdmin, false);
+  t.equal(obj.__proto__ && obj.__proto__.isAdmin, undefined);
+  t.equal(obj.prototype && obj.prototype.isAdmin, undefined);
+  t.equal(obj.constructor && obj.constructor.isAdmin, undefined);
+  t.equal(
+    obj.constructor &&
+    obj.constructor.prototype &&
+    obj.constructor.prototype.isAdmin,
+    undefined
+  );
+  t.end();
+});