diff --git a/lib/sinon/sandbox.js b/lib/sinon/sandbox.js
index 47b75eb06..385fa431d 100644
--- a/lib/sinon/sandbox.js
+++ b/lib/sinon/sandbox.js
@@ -197,18 +197,15 @@ function Sandbox() {
     };
 
     sandbox.restoreContext = function restoreContext() {
-        let injectedKeys = sandbox.injectedKeys;
-        const injectInto = sandbox.injectInto;
-
-        if (!injectedKeys) {
+        if (!sandbox.injectedKeys) {
             return;
         }
 
-        forEach(injectedKeys, function (injectedKey) {
-            delete injectInto[injectedKey];
+        forEach(sandbox.injectedKeys, function (injectedKey) {
+            delete sandbox.injectInto[injectedKey];
         });
 
-        injectedKeys = [];
+        sandbox.injectedKeys.length = 0;
     };
 
     function getFakeRestorer(object, property) {