diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst
index 96e0dc831b7956..0bd1bf386ab8fa 100644
--- a/Doc/library/multiprocessing.rst
+++ b/Doc/library/multiprocessing.rst
@@ -102,7 +102,7 @@ to start a process.  These *start methods* are
     will not be inherited.  Starting a process using this method is
     rather slow compared to using *fork* or *forkserver*.
 
-    Available on Unix and Windows.  The default on Windows.
+    Available on Unix and Windows.  The default on Windows and macOS.
 
   *fork*
     The parent process uses :func:`os.fork` to fork the Python
@@ -124,6 +124,11 @@ to start a process.  These *start methods* are
     Available on Unix platforms which support passing file descriptors
     over Unix pipes.
 
+.. versionchanged:: 3.7.4
+
+   On macOS, *spawn* start method is now the default: *fork* start method is no
+   longer reliable on macOS, see :issue:`33725`.
+
 .. versionchanged:: 3.4
    *spawn* added on all unix platforms, and *forkserver* added for
    some unix platforms.
diff --git a/Lib/multiprocessing/context.py b/Lib/multiprocessing/context.py
index c98ee434249037..29639dd880ce64 100644
--- a/Lib/multiprocessing/context.py
+++ b/Lib/multiprocessing/context.py
@@ -310,7 +310,12 @@ def _check_available(self):
         'spawn': SpawnContext(),
         'forkserver': ForkServerContext(),
     }
-    _default_context = DefaultContext(_concrete_contexts['fork'])
+    if sys.platform == 'darwin':
+        # bpo-33725: running arbitrary code after fork() is no longer reliable
+        # on macOS since macOS 10.14 (Mojave). Use spawn by default instead.
+        _default_context = DefaultContext(_concrete_contexts['spawn'])
+    else:
+        _default_context = DefaultContext(_concrete_contexts['fork'])
 
 else:
 
diff --git a/Misc/NEWS.d/next/Library/2019-05-28-01-17-42.bpo-33725.fFZoDG.rst b/Misc/NEWS.d/next/Library/2019-05-28-01-17-42.bpo-33725.fFZoDG.rst
new file mode 100644
index 00000000000000..6f1665f6fab328
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-05-28-01-17-42.bpo-33725.fFZoDG.rst
@@ -0,0 +1,2 @@
+On macOS, the :mod:`multiprocessing` module now uses *spawn* start method by
+default.