diff --git a/src/minibuf.c b/src/minibuf.c
index abc4866380..b25565d051 100644
--- a/src/minibuf.c
+++ b/src/minibuf.c
@@ -49,6 +49,10 @@ static Lisp_Object minibuf_save_list;
 
 EMACS_INT minibuf_level;
 
+/* A mutex to lock reading from the minibuffer.  */
+
+Lisp_Object minibuf_mutex;
+
 /* Fread_minibuffer leaves the input here as a string.  */
 
 Lisp_Object last_minibuf_string;
@@ -489,6 +493,7 @@ read_minibuf (Lisp_Object map, Lisp_Object initial, Lisp_Object prompt,
 
   record_unwind_protect_void (read_minibuf_unwind);
   minibuf_level++;
+  Fmutex_lock (minibuf_mutex);
   /* We are exiting the minibuffer one way or the other, so run the hook.
      It should be run before unwinding the minibuf settings.  Do it
      separately from read_minibuf_unwind because we need to make sure that
@@ -778,6 +783,7 @@ read_minibuf_unwind (void)
 
   /* If this was a recursive minibuffer,
      tie the minibuffer window back to the outer level minibuffer buffer.  */
+  Fmutex_unlock (minibuf_mutex);
   minibuf_level--;
 
   window = minibuf_window;
@@ -1877,6 +1883,10 @@ void
 syms_of_minibuf (void)
 {
   minibuf_level = 0;
+
+  minibuf_mutex = Fmake_mutex (Qnil);
+  staticpro (&minibuf_mutex);
+
   minibuf_prompt = Qnil;
   staticpro (&minibuf_prompt);