diff --git a/js/src/builtin/TestingFunctions.cpp b/js/src/builtin/TestingFunctions.cpp
index 2175ff4faedf..73f1b14cf102 100644
--- a/js/src/builtin/TestingFunctions.cpp
+++ b/js/src/builtin/TestingFunctions.cpp
@@ -5103,6 +5103,29 @@ ScriptedCallerGlobal(JSContext* cx, unsigned argc, Value* vp)
     return true;
 }
 
+static bool
+ObjectGlobal(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    RootedObject callee(cx, &args.callee());
+
+    if (!args.get(0).isObject()) {
+        ReportUsageErrorASCII(cx, callee, "Argument must be an object");
+        return false;
+    }
+
+    RootedObject obj(cx, &args[0].toObject());
+    if (IsWrapper(obj)) {
+        args.rval().setNull();
+        return true;
+    }
+
+    obj = ToWindowProxyIfWindow(&obj->global());
+
+    args.rval().setObject(*obj);
+    return true;
+}
+
 JSScript*
 js::TestingFunctionArgumentToScript(JSContext* cx,
                                     HandleValue v,
@@ -5898,6 +5921,10 @@ gc::ZealModeHelpText),
 "scriptedCallerGlobal()",
 "  Get the caller's global (or null). See JS::GetScriptedCallerGlobal.\n"),
 
+    JS_FN_HELP("objectGlobal", ObjectGlobal, 1, 0,
+"objectGlobal(obj)",
+"  Returns the object's global object or null if the object is a wrapper.\n"),
+
     JS_FN_HELP("baselineCompile", BaselineCompile, 2, 0,
 "baselineCompile([fun/code], forceDebugInstrumentation=false)",
 "  Baseline-compiles the given JS function or script.\n"
diff --git a/js/src/jit-test/tests/realms/basic.js b/js/src/jit-test/tests/realms/basic.js
index b4b15f27c8fe..62d12511ac5a 100644
--- a/js/src/jit-test/tests/realms/basic.js
+++ b/js/src/jit-test/tests/realms/basic.js
@@ -2,3 +2,9 @@ var g1 = newGlobal({sameCompartmentAs: this});
 var g2 = newGlobal({sameCompartmentAs: g1});
 g2.x = g1;
 gc();
+assertEq(objectGlobal(Math), this);
+assertEq(objectGlobal(g1.print), g1);
+assertEq(objectGlobal(g2.x), g1);
+
+// Different-compartment realms have wrappers.
+assertEq(objectGlobal(newGlobal().Math), null);