diff --git a/Doc/c-api/init.rst b/Doc/c-api/init.rst
index 2f0f20f..ed6e450 100644
--- a/Doc/c-api/init.rst
+++ b/Doc/c-api/init.rst
@@ -523,6 +523,22 @@
 :cfunc:`Py_NewInterpreter`), but mixing multiple interpreters and the
 :cfunc:`PyGILState_\*` API is unsupported.
 
+Another important thing to note about threads is their behaviour in the face
+of the C :cfunc:`fork` call. On most systems with :cfunc:`fork`, after a
+process forks only the thread that issued the fork will exist. That also
+means any locks held by other threads will never be released. Python solves
+this for :func:`os.fork` by acquiring the locks it uses internally before
+the fork, and releasing them afterwards. In addition, it resets any
+:ref:`lock-objects` in the child. When extending or embedding Python, there
+is no way to inform Python of additional (non-Python) locks that need to be
+acquired before or reset after a fork. OS facilities such as
+:cfunc:`posix_atfork` would need to be used to accomplish the same thing.
+Additionally, when extending or embedding Python, calling :cfunc:`fork`
+directly rather than through :func:`os.fork` (and returning to or calling
+into Python) may result in a deadlock by one of Python's internal locks
+being held by a thread that is defunct after the fork.
+:cfunc:`PyOS_AfterFork` tries to reset the necessary locks, but is not
+always able to.
 
 .. ctype:: PyInterpreterState
 
diff --git a/Include/import.h b/Include/import.h
index a6e2857..1b7fe0a 100644
--- a/Include/import.h
+++ b/Include/import.h
@@ -27,6 +27,14 @@
 PyAPI_FUNC(void) PyImport_Cleanup(void);
 PyAPI_FUNC(int) PyImport_ImportFrozenModule(char *);
 
+#ifdef WITH_THREAD
+PyAPI_FUNC(void) _PyImport_AcquireLock(void);
+PyAPI_FUNC(int) _PyImport_ReleaseLock(void);
+#else
+#define _PyImport_AcquireLock()
+#define _PyImport_ReleaseLock() 1
+#endif
+
 PyAPI_FUNC(struct filedescr *) _PyImport_FindModule(
 	const char *, PyObject *, char *, size_t, FILE **, PyObject **);
 PyAPI_FUNC(int) _PyImport_IsScript(struct filedescr *);
diff --git a/Lib/test/test_fork1.py b/Lib/test/test_fork1.py
index b42304b..22e6f31 100644
--- a/Lib/test/test_fork1.py
+++ b/Lib/test/test_fork1.py
@@ -1,8 +1,14 @@
 """This test checks for correct fork() behavior.
 """
 
+import errno
+import imp
 import os
+import signal
+import sys
 import time
+import threading
+
 from test.fork_wait import ForkWait
 from test.test_support import run_unittest, reap_children, get_attribute
 
@@ -23,6 +29,41 @@
         self.assertEqual(spid, cpid)
         self.assertEqual(status, 0, "cause = %d, exit = %d" % (status&0xff, status>>8))
 
+    def test_import_lock_fork(self):
+        import_started = threading.Event()
+        fake_module_name = "fake test module"
+        partial_module = "partial"
+        complete_module = "complete"
+        def importer():
+            imp.acquire_lock()
+            sys.modules[fake_module_name] = partial_module
+            import_started.set()
+            time.sleep(0.01) # Give the other thread time to try and acquire.
+            sys.modules[fake_module_name] = complete_module
+            imp.release_lock()
+        t = threading.Thread(target=importer)
+        t.start()
+        import_started.wait()
+        pid = os.fork()
+        try:
+            if not pid:
+                m = __import__(fake_module_name)
+                if m == complete_module:
+                    os._exit(0)
+                else:
+                    os._exit(1)
+            else:
+                t.join()
+                # Exitcode 1 means the child got a partial module (bad.) No
+                # exitcode (but a hang, which manifests as 'got pid 0')
+                # means the child deadlocked (also bad.)
+                self.wait_impl(pid)
+        finally:
+            try:
+                os.kill(pid, signal.SIGKILL)
+            except OSError:
+                pass
+
 def test_main():
     run_unittest(ForkTest)
     reap_children()
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 19c809d..0d2ca54 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -3603,11 +3603,21 @@
 static PyObject *
 posix_fork1(PyObject *self, PyObject *noargs)
 {
-	pid_t pid = fork1();
+	pid_t pid;
+	int result;
+	_PyImport_AcquireLock();
+	pid = fork1();
+	result = _PyImport_ReleaseLock();
 	if (pid == -1)
 		return posix_error();
 	if (pid == 0)
 		PyOS_AfterFork();
+	if (result < 0) {
+		/* Don't clobber the OSError if the fork failed. */
+		PyErr_SetString(PyExc_RuntimeError,
+				"not holding the import lock");
+		return NULL;
+	}
 	return PyLong_FromPid(pid);
 }
 #endif
@@ -3622,11 +3632,21 @@
 static PyObject *
 posix_fork(PyObject *self, PyObject *noargs)
 {
-	pid_t pid = fork();
+	pid_t pid;
+	int result;
+	_PyImport_AcquireLock();
+	pid = fork();
+	result = _PyImport_ReleaseLock();
 	if (pid == -1)
 		return posix_error();
 	if (pid == 0)
 		PyOS_AfterFork();
+	if (result < 0) {
+		/* Don't clobber the OSError if the fork failed. */
+		PyErr_SetString(PyExc_RuntimeError,
+				"not holding the import lock");
+		return NULL;
+	}
 	return PyLong_FromPid(pid);
 }
 #endif
@@ -3729,14 +3749,22 @@
 static PyObject *
 posix_forkpty(PyObject *self, PyObject *noargs)
 {
-	int master_fd = -1;
+	int master_fd = -1, result;
 	pid_t pid;
 
+	_PyImport_AcquireLock();
 	pid = forkpty(&master_fd, NULL, NULL, NULL);
+	result = _PyImport_ReleaseLock();
 	if (pid == -1)
 		return posix_error();
 	if (pid == 0)
 		PyOS_AfterFork();
+	if (result < 0) {
+		/* Don't clobber the OSError if the fork failed. */
+		PyErr_SetString(PyExc_RuntimeError,
+				"not holding the import lock");
+		return NULL;
+	}
 	return Py_BuildValue("(Ni)", PyLong_FromPid(pid), master_fd);
 }
 #endif
diff --git a/Python/import.c b/Python/import.c
index 055f081..3ca452a 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -258,8 +258,8 @@
 static long import_lock_thread = -1;
 static int import_lock_level = 0;
 
-static void
-lock_import(void)
+void
+_PyImport_AcquireLock(void)
 {
 	long me = PyThread_get_thread_ident();
 	if (me == -1)
@@ -283,8 +283,8 @@
 	import_lock_level = 1;
 }
 
-static int
-unlock_import(void)
+int
+_PyImport_ReleaseLock(void)
 {
 	long me = PyThread_get_thread_ident();
 	if (me == -1 || import_lock == NULL)
@@ -299,23 +299,16 @@
 	return 1;
 }
 
-/* This function is called from PyOS_AfterFork to ensure that newly
-   created child processes do not share locks with the parent. */
+/* This function used to be called from PyOS_AfterFork to ensure that newly
+   created child processes do not share locks with the parent, but for some
+   reason only on AIX systems. Instead of re-initializing the lock, we now
+   acquire the import lock around fork() calls. */
 
 void
 _PyImport_ReInitLock(void)
 {
-#ifdef _AIX
-	if (import_lock != NULL)
-		import_lock = PyThread_allocate_lock();
-#endif
 }
 
-#else
-
-#define lock_import()
-#define unlock_import() 0
-
 #endif
 
 static PyObject *
@@ -332,7 +325,7 @@
 imp_acquire_lock(PyObject *self, PyObject *noargs)
 {
 #ifdef WITH_THREAD
-	lock_import();
+	_PyImport_AcquireLock();
 #endif
 	Py_INCREF(Py_None);
 	return Py_None;
@@ -342,7 +335,7 @@
 imp_release_lock(PyObject *self, PyObject *noargs)
 {
 #ifdef WITH_THREAD
-	if (unlock_import() < 0) {
+	if (_PyImport_ReleaseLock() < 0) {
 		PyErr_SetString(PyExc_RuntimeError,
 				"not holding the import lock");
 		return NULL;
@@ -2185,9 +2178,9 @@
 			 PyObject *fromlist, int level)
 {
 	PyObject *result;
-	lock_import();
+	_PyImport_AcquireLock();
 	result = import_module_level(name, globals, locals, fromlist, level);
-	if (unlock_import() < 0) {
+	if (_PyImport_ReleaseLock() < 0) {
 		Py_XDECREF(result);
 		PyErr_SetString(PyExc_RuntimeError,
 				"not holding the import lock");