diff --git a/js/xpconnect/src/Sandbox.cpp b/js/xpconnect/src/Sandbox.cpp
index cfbd97f69b8..87411414dfe 100644
--- a/js/xpconnect/src/Sandbox.cpp
+++ b/js/xpconnect/src/Sandbox.cpp
@@ -1507,9 +1507,8 @@ xpc::EvalInSandbox(JSContext *cx, HandleObject sandboxArg, const nsAString& sour
         JSAutoCompartment ac(sandcx, sandbox);
 
         JS::CompileOptions options(sandcx);
-        options.setFileAndLine(filenameBuf.get(), lineNo);
-        if (jsVersion != JSVERSION_DEFAULT)
-               options.setVersion(jsVersion);
+        options.setFileAndLine(filenameBuf.get(), lineNo)
+               .setVersion(jsVersion);
         JS::RootedObject rootedSandbox(sandcx, sandbox);
         ok = JS::Evaluate(sandcx, rootedSandbox, options,
                           PromiseFlatString(source).get(), source.Length(), &v);
diff --git a/js/xpconnect/tests/chrome/test_evalInSandbox.xul b/js/xpconnect/tests/chrome/test_evalInSandbox.xul
index 75607cabce1..dc5e969987f 100644
--- a/js/xpconnect/tests/chrome/test_evalInSandbox.xul
+++ b/js/xpconnect/tests/chrome/test_evalInSandbox.xul
@@ -151,6 +151,33 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=533596
         ok(false, "sameZoneAs works");
       }
 
+      // The 'let' keyword only appears with JS 1.7 and above. We use this fact
+      // to make sure that sandboxes get explict JS versions and don't inherit
+      // them from the most recent scripted frame.
+      function checkExplicitVersions() {
+        const Cu = Components.utils;
+        var sb = new Cu.Sandbox(sop);
+        Cu.evalInSandbox('let someVariable = 42', sb, '1.7');
+        ok(true, "Didn't throw with let");
+        try {
+          Cu.evalInSandbox('let someVariable = 42', sb);
+          ok(false, "Should have thrown with let");
+        } catch (e) {
+          ok(true, "Threw with let: " + e);
+        }
+        try {
+          Cu.evalInSandbox('let someVariable = 42', sb, '1.5');
+          ok(false, "Should have thrown with let");
+        } catch (e) {
+          ok(true, "Threw with let: " + e);
+        }
+      }
+      var outerSB = new Cu.Sandbox(this);
+      Cu.evalInSandbox(checkExplicitVersions.toSource(), outerSB, '1.7');
+      outerSB.ok = ok;
+      outerSB.sop = this;
+      Cu.evalInSandbox('checkExplicitVersions();', outerSB);
+
       Cu.import("resource://gre/modules/jsdebugger.jsm");
       addDebuggerToGlobal(this);