diff --git a/CWRU/CWRU.chlog b/CWRU/CWRU.chlog
index e00f732a..a4436be1 100644
--- a/CWRU/CWRU.chlog
+++ b/CWRU/CWRU.chlog
@@ -8598,3 +8598,15 @@ subst.c
 	- valid_parameter_transform: new function, reject transformations
 	  longer than a single character or invalid transformation operators
 	- parameter_brace_transform: call valid_parameter_transform
+
+				   6/22
+				   ----
+lib/sh/zread.c
+	- lbuf: bump size up to ZBUFSIZ (default 4096). From a report by
+	  Jason A. Donenfeld <Jason@zx2c4.com>
+
+lib/sh/zcatfd.c
+	- zcatfd: lbuf: bump size up to ZBUFSIZ (default 4096)
+
+lib/sh/zmapfd.c
+	- zmapfd: lbuf: bump size up to ZBUFSIZ (default 4096)
diff --git a/lib/sh/zcatfd.c b/lib/sh/zcatfd.c
index f9a2322e..aa8199fd 100644
--- a/lib/sh/zcatfd.c
+++ b/lib/sh/zcatfd.c
@@ -34,6 +34,10 @@
 extern int errno;
 #endif
 
+#ifndef ZBUFSIZ
+#  define ZBUFSIZ 4096
+#endif
+
 extern ssize_t zread PARAMS((int, char *, size_t));
 extern int zwrite PARAMS((int, char *, ssize_t));
 
@@ -46,7 +50,7 @@ zcatfd (fd, ofd, fn)
 {
   ssize_t nr;
   int rval;
-  char lbuf[1024];
+  char lbuf[ZBUFSIZ];
 
   rval = 0;
   while (1)
diff --git a/lib/sh/zmapfd.c b/lib/sh/zmapfd.c
index f3fb8473..f9e9ed71 100644
--- a/lib/sh/zmapfd.c
+++ b/lib/sh/zmapfd.c
@@ -36,6 +36,10 @@
 extern int errno;
 #endif
 
+#ifndef ZBUFSIZ
+#  define ZBUFSIZ 4096
+#endif
+
 extern ssize_t zread PARAMS((int, char *, size_t));
 
 /* Dump contents of file descriptor FD to *OSTR.  FN is the filename for
@@ -48,12 +52,12 @@ zmapfd (fd, ostr, fn)
 {
   ssize_t nr;
   int rval;
-  char lbuf[512];
+  char lbuf[ZBUFSIZ];
   char *result;
   int rsize, rind;
 
   rval = 0;
-  result = (char *)xmalloc (rsize = 512);
+  result = (char *)xmalloc (rsize = ZBUFSIZ);
   rind = 0;
 
   while (1)
@@ -72,7 +76,7 @@ zmapfd (fd, ostr, fn)
 	  return -1;
 	}
 
-      RESIZE_MALLOCED_BUFFER (result, rind, nr, rsize, 512);
+      RESIZE_MALLOCED_BUFFER (result, rind, nr, rsize, ZBUFSIZ);
       memcpy (result+rind, lbuf, nr);
       rind += nr;
     }
diff --git a/lib/sh/zread.c b/lib/sh/zread.c
index 8dd78102..71a06a76 100644
--- a/lib/sh/zread.c
+++ b/lib/sh/zread.c
@@ -1,6 +1,6 @@
 /* zread - read data from file descriptor into buffer with retries */
 
-/* Copyright (C) 1999-2017 Free Software Foundation, Inc.
+/* Copyright (C) 1999-2020 Free Software Foundation, Inc.
 
    This file is part of GNU Bash, the Bourne Again SHell.
 
@@ -37,6 +37,10 @@ extern int errno;
 #  define SEEK_CUR 1
 #endif
 
+#ifndef ZBUFSIZ
+#  define ZBUFSIZ 4096
+#endif
+
 extern int executing_builtin;
 
 extern void check_signals_and_traps (void);
@@ -117,7 +121,7 @@ zreadintr (fd, buf, len)
    in read(2).  This does some local buffering to avoid many one-character
    calls to read(2), like those the `read' builtin performs. */
 
-static char lbuf[128];
+static char lbuf[ZBUFSIZ];
 static size_t lind, lused;
 
 ssize_t