diff --git a/src/compile.cpp b/src/compile.cpp
index ee41dd9cb7..48ab0aebeb 100644
--- a/src/compile.cpp
+++ b/src/compile.cpp
@@ -5984,9 +5984,11 @@ class MyProcessor: public Processor {
   virtual void
   initVtable(Thread* t, object c)
   {
+    PROTECT(t, c);
     for (int i = classLength(t, c) - 1; i >= 0; --i) {
-      classVtable(t, c, i) = reinterpret_cast<void*>
+      void* thunk = reinterpret_cast<void*>
         (virtualThunk(static_cast<MyThread*>(t), i));
+      classVtable(t, c, i) = thunk;
     }
   }
 
diff --git a/src/machine.cpp b/src/machine.cpp
index 9b8ddb7c38..574b5ffd99 100644
--- a/src/machine.cpp
+++ b/src/machine.cpp
@@ -2439,6 +2439,8 @@ parseClass(Thread* t, const uint8_t* data, unsigned size)
      classLoader(t, class_),
      vtableLength);
 
+  PROTECT(t, real);
+
   t->m->processor->initVtable(t, real);
 
   updateClassTables(t, real, class_);