diff --git a/stage0/src/runtime/compact.cpp b/stage0/src/runtime/compact.cpp
index 2d5ecf1e8c..f35b846480 100644
--- a/stage0/src/runtime/compact.cpp
+++ b/stage0/src/runtime/compact.cpp
@@ -89,6 +89,7 @@ void * object_compactor::alloc(size_t sz) {
         m_begin    = new_begin;
     }
     void * r = m_end;
+    memset(r, 0, sz);
     m_end = static_cast<char*>(m_end) + sz;
     lean_assert(m_end <= m_capacity);
     return r;