diff -ruN orig/ChangeLog src/ChangeLog
--- orig/ChangeLog
+++ src/ChangeLog
@@ -1,6 +1,10 @@
 
                 ChangeLog file for zlib
 
+Changes in 1.2.12 (Qt) (28 Mar 2022)
+- This is a stripped down copy of zlib that contains patches to
+  make it compile as part of Qt. See also "qtpatches.diff".
+
 Changes in 1.2.12 (27 Mar 2022)
 - Cygwin does not have _wopen(), so do not create gzopen_w() there
 - Permit a deflateParams() parameter change as soon as possible
diff -ruN orig/gzguts.h src/gzguts.h
--- orig/gzguts.h
+++ src/gzguts.h
@@ -3,6 +3,12 @@
  * For conditions of distribution and use, see copyright notice in zlib.h
  */
 
+#include <qconfig.h>
+
+#ifdef QT_VISIBILITY_AVAILABLE
+#define HAVE_HIDDEN
+#endif
+
 #ifdef _LARGEFILE64_SOURCE
 #  ifndef _LARGEFILE_SOURCE
 #    define _LARGEFILE_SOURCE 1
diff -ruN orig/README src/README
--- orig/README
+++ src/README
@@ -6,6 +6,9 @@
 http://tools.ietf.org/html/rfc1950 (zlib format), rfc1951 (deflate format) and
 rfc1952 (gzip format).
 
+This is a stripped down copy of zlib that contains patches to make it compile
+as part of Qt. See also "qtpatches.diff".
+
 All functions of the compression library are documented in the file zlib.h
 (volunteer to write man pages welcome, contact zlib@gzip.org).  A usage example
 of the library is given in the file test/example.c which also tests that
diff -ruN orig/zconf.h src/zconf.h
--- orig/zconf.h
+++ src/zconf.h
@@ -8,6 +8,9 @@
 #ifndef ZCONF_H
 #define ZCONF_H
 
+/* Since Qt Core must export these symbols, define Z_PREFIX to avoid clashes system zlib */
+#define Z_PREFIX
+
 /*
  * If you *really* need a unique prefix for all types and library functions,
  * compile with -DZ_PREFIX. The "standard" zlib should be compiled without it.
@@ -136,6 +139,7 @@
 #  endif
 #  define zlibCompileFlags      z_zlibCompileFlags
 #  define zlibVersion           z_zlibVersion
+#  define z_errmsg              z_z_errmsg
 
 /* all zlib typedefs in zlib.h and zconf.h */
 #  define Byte                  z_Byte
@@ -431,7 +435,7 @@
    typedef unsigned long z_crc_t;
 #endif
 
-#ifdef HAVE_UNISTD_H    /* may be set to #if 1 by ./configure */
+#if defined(HAVE_UNISTD_H) || !defined(WIN32)
 #  define Z_HAVE_UNISTD_H
 #endif
 
diff -ruN orig/zlib.h src/zlib.h
--- orig/zlib.h
+++ src/zlib.h
@@ -33,11 +33,15 @@
 
 #include "zconf.h"
 
+#include <qglobal.h>
+#undef ZEXTERN
+#define ZEXTERN Q_CORE_EXPORT
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#define ZLIB_VERSION "1.2.12"
+#define ZLIB_VERSION "1.2.12 (Qt)"
 #define ZLIB_VERNUM 0x12c0
 #define ZLIB_VER_MAJOR 1
 #define ZLIB_VER_MINOR 2
diff -ruN orig/zutil.h src/zutil.h
--- orig/zutil.h
+++ src/zutil.h
@@ -13,6 +13,12 @@
 #ifndef ZUTIL_H
 #define ZUTIL_H
 
+#include <qconfig.h>
+
+#ifdef QT_VISIBILITY_AVAILABLE
+#define HAVE_HIDDEN
+#endif
+
 #ifdef HAVE_HIDDEN
 #  define ZLIB_INTERNAL __attribute__((visibility ("hidden")))
 #else
@@ -143,6 +149,11 @@
 #    if defined(__MWERKS__) && __dest_os != __be_os && __dest_os != __win32_os
 #      include <unix.h> /* for fdopen */
 #    else
+//     We need to include stdio.h here because zlib.h will include TargetConditionals.h
+//     This will define TARGET_OS_MAC that leads to this check.
+//     Since zutil.h will include gzguts.h and gzguts.h includes stdio.h
+//     AFTER check for fdopen we need to include stdio.h directly
+#      include <stdio.h>
 #      ifndef fdopen
 #        define fdopen(fd,mode) NULL /* No fdopen() */
 #      endif
@@ -166,7 +177,7 @@
 #  define OS_CODE 18
 #endif
 
-#ifdef __APPLE__
+#if defined(__APPLE__) && !defined(OS_CODE)
 #  define OS_CODE 19
 #endif