--- a/src/code/target-thread.lisp
+++ b/src/code/target-thread.lisp
@@ -219,6 +219,14 @@
 potentially stale even before the function returns, as the thread may exit at
 any time."
   (thread-%alive-p thread))
+(defun thread-emphemeral-p (thread)
+  #!+sb-doc
+  "Return T if THREAD is `ephemeral', which indicates that this thread is
+used by SBCL for internal purposes, and specifically that it knows how to
+to terminate this thread cleanly prior to core file saving without signalling
+an error in that case."
+  (thread-%ephemeral-p thread))
 ;; A thread is eligible for gc iff it has finished and there are no
 ;; more references to it. This list is supposed to keep a reference to
@@ -1341,7 +1349,7 @@
 ;;;; The beef
-(defun make-thread (function &key name arguments)
+(defun make-thread (function &key name arguments ephemeral)
   "Create a new thread of NAME that runs FUNCTION with the argument
 list designator provided (defaults to no argument). Thread exits when
@@ -1362,7 +1370,7 @@
      (with-mutex (*make-thread-lock*)
-       (let* ((thread (%make-thread :name name))
+       (let* ((thread (%make-thread :name name :%ephemeral-p ephemeral))
               (setup-sem (make-semaphore :name "Thread setup semaphore"))
               (real-function (coerce function 'function))
               (arguments     (if (listp arguments)