diff --git a/Include/intrcheck.h b/Include/intrcheck.h
index f9658e28b14..85660516900 100644
--- a/Include/intrcheck.h
+++ b/Include/intrcheck.h
@@ -37,6 +37,7 @@ PERFORMANCE OF THIS SOFTWARE.
 
 extern int PyOS_InterruptOccurred Py_PROTO((void));
 extern void PyOS_InitInterrupts Py_PROTO((void));
+void PyOS_AfterFork Py_PROTO((void));
 
 #ifdef __cplusplus
 }
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index e06827aa720..58111efda5e 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -1082,6 +1082,7 @@ posix_fork(self, args)
 	pid = fork();
 	if (pid == -1)
 		return posix_error();
+	PyOS_AfterFork();
 	return PyInt_FromLong((long)pid);
 }
 #endif
diff --git a/Modules/signalmodule.c b/Modules/signalmodule.c
index e8154925278..e91c3cb6f60 100644
--- a/Modules/signalmodule.c
+++ b/Modules/signalmodule.c
@@ -613,3 +613,12 @@ PyOS_InterruptOccurred()
 	}
 	return 0;
 }
+
+void
+PyOS_AfterFork()
+{
+#ifdef WITH_THREAD
+	main_thread = get_thread_ident();
+	main_pid = getpid();
+#endif
+}
diff --git a/Parser/intrcheck.c b/Parser/intrcheck.c
index a2a31452bb4..7fe6205f444 100644
--- a/Parser/intrcheck.c
+++ b/Parser/intrcheck.c
@@ -219,3 +219,8 @@ PyOS_InterruptOccurred()
 }
 
 #endif /* !OK */
+
+void
+PyOS_AfterFork()
+{
+}