diff --git a/src/thread.c b/src/thread.c
index ee93a7a8644..00876ff3392 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -904,7 +904,7 @@ If NAME is given, it must be a string; it names the new thread.  */)
   new_thread->m_current_buffer = current_thread->m_current_buffer;
 
   ptrdiff_t size = 50;
-  union specbinding *pdlvec = xmalloc ((1 + size) * sizeof (union specbinding));
+  union specbinding *pdlvec = xzalloc ((1 + size) * sizeof (union specbinding));
   new_thread->m_specpdl = pdlvec + 1;  /* Skip the dummy entry.  */
   new_thread->m_specpdl_end = new_thread->m_specpdl + size;
   new_thread->m_specpdl_ptr = new_thread->m_specpdl;