Index: Python/import.c
===================================================================
--- Python/import.c	(revision 74154)
+++ Python/import.c	(working copy)
@@ -256,8 +256,8 @@
 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)
@@ -281,8 +281,8 @@
 	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)
@@ -303,17 +303,8 @@
 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 *
@@ -330,7 +321,7 @@
 imp_acquire_lock(PyObject *self, PyObject *noargs)
 {
 #ifdef WITH_THREAD
-	lock_import();
+	_PyImport_AcquireLock();
 #endif
 	Py_INCREF(Py_None);
 	return Py_None;
@@ -340,7 +331,7 @@
 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;
@@ -2183,9 +2174,9 @@
 			 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");
Index: Include/import.h
===================================================================
--- Include/import.h	(revision 74154)
+++ Include/import.h	(working copy)
@@ -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 *);
Index: Lib/test/test_fork1.py
===================================================================
--- Lib/test/test_fork1.py	(revision 74154)
+++ Lib/test/test_fork1.py	(working copy)
@@ -1,11 +1,18 @@
 """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 TestSkipped, run_unittest, reap_children
 
+
 try:
     os.fork
 except AttributeError:
@@ -24,6 +31,41 @@
         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()
Index: Modules/posixmodule.c
===================================================================
--- Modules/posixmodule.c	(revision 74154)
+++ Modules/posixmodule.c	(working copy)
@@ -3630,7 +3630,11 @@
 static PyObject *
 posix_fork1(PyObject *self, PyObject *noargs)
 {
-	pid_t pid = fork1();
+	pid_t pid;
+	_PyImport_AcquireLock();
+	pid = fork1();
+	/* XXX(twouters): check PyImport_ReleaseLock's return value? */
+	_PyImport_ReleaseLock();
 	if (pid == -1)
 		return posix_error();
 	if (pid == 0)
@@ -3649,7 +3653,11 @@
 static PyObject *
 posix_fork(PyObject *self, PyObject *noargs)
 {
-	pid_t pid = fork();
+	pid_t pid;
+	_PyImport_AcquireLock();
+	pid = fork();
+	/* XXX(twouters): check PyImport_ReleaseLock's return value? */
+	_PyImport_ReleaseLock();
 	if (pid == -1)
 		return posix_error();
 	if (pid == 0)
@@ -3759,7 +3767,10 @@
 	int master_fd = -1;
 	pid_t pid;
 
+	_PyImport_AcquireLock();
 	pid = forkpty(&master_fd, NULL, NULL, NULL);
+	/* XXX(twouters): check PyImport_ReleaseLock's return value? */
+	_PyImport_ReleaseLock();
 	if (pid == -1)
 		return posix_error();
 	if (pid == 0)