diff --git a/js/src/builtin/TypedObject.cpp b/js/src/builtin/TypedObject.cpp
index e223cc3dbdfe..0feb9a87a624 100644
--- a/js/src/builtin/TypedObject.cpp
+++ b/js/src/builtin/TypedObject.cpp
@@ -911,6 +911,12 @@ StructMetaTypeDescr::layout(JSContext *cx,
             return false;
     }
 
+    if (!JSObject::freeze(cx, fieldOffsets))
+        return false;
+
+    if (!JSObject::freeze(cx, fieldTypes))
+        return false;
+
     RootedValue fieldOffsetsValue(cx, ObjectValue(*fieldOffsets));
     if (!JSObject::defineProperty(cx, structType, cx->names().fieldOffsets,
                                   fieldOffsetsValue, nullptr, nullptr,
diff --git a/js/src/tests/ecma_6/TypedObject/structtypereflection.js b/js/src/tests/ecma_6/TypedObject/structtypereflection.js
index 9305f95019a9..44b450500cba 100644
--- a/js/src/tests/ecma_6/TypedObject/structtypereflection.js
+++ b/js/src/tests/ecma_6/TypedObject/structtypereflection.js
@@ -36,6 +36,10 @@ function runTests() {
     assertEq(S.fieldOffsets.y, 4);
     assertEq(S.fieldOffsets.z, 8);
 
+    // fieldTypes and fieldOffsets should be frozen
+    assertEq(Object.isFrozen(S.fieldTypes), true);
+    assertEq(Object.isFrozen(S.fieldOffsets), true);
+
     if (typeof reportCompare === "function")
         reportCompare(true, true);
     print("Tests complete");