diff --git a/deps/zlib/zutil.h b/deps/zlib/zutil.h
index b079ea6a80f5ab..9c5376ca810b36 100644
--- a/deps/zlib/zutil.h
+++ b/deps/zlib/zutil.h
@@ -100,38 +100,28 @@ extern z_const char * const z_errmsg[10]; /* indexed by 2-zlib_error */
 #endif
 
 #ifdef AMIGA
-#  define OS_CODE  1
+#  define OS_CODE  0x01
 #endif
 
 #if defined(VAXC) || defined(VMS)
-#  define OS_CODE  2
+#  define OS_CODE  0x02
 #  define F_OPEN(name, mode) \
      fopen((name), (mode), "mbc=60", "ctx=stm", "rfm=fix", "mrs=512")
 #endif
 
-#ifdef __370__
-#  if __TARGET_LIB__ < 0x20000000
-#    define OS_CODE 4
-#  elif __TARGET_LIB__ < 0x40000000
-#    define OS_CODE 11
-#  else
-#    define OS_CODE 8
-#  endif
-#endif
-
 #if defined(ATARI) || defined(atarist)
-#  define OS_CODE  5
+#  define OS_CODE  0x05
 #endif
 
 #ifdef OS2
-#  define OS_CODE  6
+#  define OS_CODE  0x06
 #  if defined(M_I86) && !defined(Z_SOLO)
 #    include <malloc.h>
 #  endif
 #endif
 
 #if defined(MACOS) || defined(TARGET_OS_MAC)
-#  define OS_CODE  7
+#  define OS_CODE  0x07
 #  ifndef Z_SOLO
 #    if defined(__MWERKS__) && __dest_os != __be_os && __dest_os != __win32_os
 #      include <unix.h> /* for fdopen */
@@ -143,24 +133,18 @@ extern z_const char * const z_errmsg[10]; /* indexed by 2-zlib_error */
 #  endif
 #endif
 
-#ifdef __acorn
-#  define OS_CODE 13
+#ifdef TOPS20
+#  define OS_CODE  0x0a
 #endif
 
-#if defined(WIN32) && !defined(__CYGWIN__)
-#  define OS_CODE  10
-#endif
-
-#ifdef _BEOS_
-#  define OS_CODE  16
-#endif
-
-#ifdef __TOS_OS400__
-#  define OS_CODE 18
+#ifdef WIN32
+#  ifndef __CYGWIN__  /* Cygwin is Unix, not Win32 */
+#    define OS_CODE  0x0b
+#  endif
 #endif
 
-#ifdef __APPLE__
-#  define OS_CODE 19
+#ifdef __50SERIES /* Prime/PRIMOS */
+#  define OS_CODE  0x0f
 #endif
 
 #if defined(_BEOS_) || defined(RISCOS)
@@ -195,7 +179,7 @@ extern z_const char * const z_errmsg[10]; /* indexed by 2-zlib_error */
         /* common defaults */
 
 #ifndef OS_CODE
-#  define OS_CODE  3     /* assume Unix */
+#  define OS_CODE  0x03  /* assume Unix */
 #endif
 
 #ifndef F_OPEN
diff --git a/test/parallel/test-zlib-oscode.js b/test/parallel/test-zlib-oscode.js
new file mode 100644
index 00000000000000..668007005dc21d
--- /dev/null
+++ b/test/parallel/test-zlib-oscode.js
@@ -0,0 +1,22 @@
+'use strict';
+
+const common = require('../common');
+
+// Assert that the zlib output on MacOS and Linux is identical to what it was
+// before the zlib 1.2.11 update. The change was in an unused 'OS code' in the
+// header, so is not dependent on the size or content of the data encrypted.
+// The test doesn't apply to non-MacOS/Linux platforms, they already had unique
+// OS codes prior to the zlib update.
+
+if (process.platform !== 'linux' && process.platform !== 'darwin')
+  return common.skip('test applies only to Mac and Linux');
+
+const assert = require('assert');
+const zlib = require('zlib');
+
+const expected = '1f8b0800000000000003ab00008316dc8c01000000';
+const options = {strategy: zlib.Z_DEFAULT_STRATEGY};
+
+zlib.gzip('x', options, common.mustCall(function(err, compressed) {
+  assert.strictEqual(compressed.toString('hex'), expected);
+}));