diff -r c080ef5989f7 Modules/socketmodule.c
--- a/Modules/socketmodule.c	Fri Jan 29 19:09:41 2016 -0600
+++ b/Modules/socketmodule.c	Tue Feb 09 21:37:13 2016 -0500
@@ -183,15 +183,66 @@
 #ifdef HAVE_SYS_PARAM_H
 #include <sys/param.h>
 #endif
+
+#if defined(WITH_THREAD) && defined(__APPLE__)
+#include <sys/utsname.h>
+
+#define USE_GETADDRINFO_LOCK_APPLE
+
+static int needs_getaddrinfo_lock = -1;
+
+/* Determine if we must lock around getaddrinfo on Mac OS X.
+
+   getaddrinfo is thread-safe on Mac OS X 10.5 and later. Originally it was
+   a mix of code including an unsafe implementation from an old BSD's
+   libresolv. In 10.5 Apple reimplemented it as a safe IPC call to the
+   mDNSResponder process. 10.5 is the first be UNIX '03 certified, which
+   includes the requirement that getaddrinfo be thread-safe.
+
+   See issue #25924 for details. */
+static int
+set_needs_getaddrinfo_lock(void)
+{
+    struct utsname names;
+    int ret, major, minor, patch;
+
+    /* "sysctlbyname" wasn't found to work on Mac OS 10.4, but uname should */
+    ret = uname(&names);
+    if (ret < 0) {
+        PyErr_Format(PyExc_ImportError, "uname failed: error code %d", ret);
+        return -1;
+    }
+
+    /* parse release string: "x.y.z" */
+    ret = sscanf(names.release, "%d.%d.%d", &major, &minor, &patch);
+    if (ret != 3) {
+        PyErr_Format(PyExc_ImportError,
+                     "Cannot parse uname: \"%s\"", names.release);
+        return -1;
+    }
+
+    needs_getaddrinfo_lock = ((major * 100 + minor) < 105);  /* before 10.5? */
+
+    return 0;
+}
+
+#else
 /* On systems on which getaddrinfo() is believed to not be thread-safe,
    (this includes the getaddrinfo emulation) protect access with a lock. */
-#if defined(WITH_THREAD) && (defined(__APPLE__) || \
+#if defined(WITH_THREAD) && (
     (defined(__FreeBSD__) && __FreeBSD_version+0 < 503000) || \
     defined(__OpenBSD__) || defined(__NetBSD__) || \
     !defined(HAVE_GETADDRINFO))
 #define USE_GETADDRINFO_LOCK
 #endif
-
+#endif
+
+#ifdef USE_GETADDRINFO_LOCK_APPLE
+#define ACQUIRE_GETADDRINFO_LOCK \
+    if (needs_getaddrinfo_lock) { PyThread_acquire_lock(netdb_lock, 1); }
+#define RELEASE_GETADDRINFO_LOCK \
+    if (needs_getaddrinfo_lock) { PyThread_release_lock(netdb_lock); }
+#else
 #ifdef USE_GETADDRINFO_LOCK
 #define ACQUIRE_GETADDRINFO_LOCK PyThread_acquire_lock(netdb_lock, 1);
 #define RELEASE_GETADDRINFO_LOCK PyThread_release_lock(netdb_lock);
@@ -199,6 +250,7 @@
 #define ACQUIRE_GETADDRINFO_LOCK
 #define RELEASE_GETADDRINFO_LOCK
 #endif
+#endif
 
 #if defined(USE_GETHOSTBYNAME_LOCK) || defined(USE_GETADDRINFO_LOCK)
 # include "pythread.h"
@@ -6091,6 +6143,12 @@
     if (!os_init())
         return NULL;
 
+#if defined(WITH_THREAD) && defined(__APPLE__)
+    if (set_needs_getaddrinfo_lock() != 0) {
+        return NULL;
+    }
+#endif
+
 #ifdef MS_WINDOWS
     if (support_wsa_no_inherit == -1) {
 #if defined(_MSC_VER) && _MSC_VER >= 1800