1 files changed, 14 insertions, 4 deletions

diff --git a/src/data.c b/src/data.c
index 605a5f43af7..c8beeda7208 100644
--- a/src/data.c
+++ b/src/data.c
@@ -1713,11 +1713,21 @@ set_default_internal (Lisp_Object symbol, Lisp_Object value,
                set it in the buffers that don't nominally have a local value.  */
             if (idx > 0)
               {
-                struct buffer *b;
+                Lisp_Object buf, tail;
+
+                /* Do this only in live buffers, so that if there are
+                   a lot of buffers which are dead, that doesn't slow
+                   down let-binding of variables that are
+                   automatically local when set, like
+                   case-fold-search.  This is for Lisp programs that
+                   let-bind such variables in their inner loops.  */
+                FOR_EACH_LIVE_BUFFER (tail, buf)
+                  {
+                    struct buffer *b = XBUFFER (buf);
 
-                FOR_EACH_BUFFER (b)
-                  if (!PER_BUFFER_VALUE_P (b, idx))
-                    set_per_buffer_value (b, offset, value);
+                    if (!PER_BUFFER_VALUE_P (b, idx))
+                      set_per_buffer_value (b, offset, value);
+                  }
               }
           }
         else