diff --git a/mercurial/cext/osutil.c b/mercurial/cext/osutil.c
--- a/mercurial/cext/osutil.c
+++ b/mercurial/cext/osutil.c
@@ -20,6 +20,7 @@
 #include <windows.h>
 #else
 #include <dirent.h>
+#include <signal.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ -1111,6 +1112,25 @@
 }
 #endif /* defined(HAVE_LINUX_STATFS) || defined(HAVE_BSD_STATFS) */
 
+static PyObject *unblocksignal(PyObject *self, PyObject *args)
+{
+	int sig = 0;
+	int r;
+	if (!PyArg_ParseTuple(args, "i", &sig))
+		return NULL;
+	sigset_t set;
+	r = sigemptyset(&set);
+	if (r != 0)
+		return PyErr_SetFromErrno(PyExc_OSError);
+	r = sigaddset(&set, sig);
+	if (r != 0)
+		return PyErr_SetFromErrno(PyExc_OSError);
+	r = sigprocmask(SIG_UNBLOCK, &set, NULL);
+	if (r != 0)
+		return PyErr_SetFromErrno(PyExc_OSError);
+	Py_RETURN_NONE;
+}
+
 #endif /* ndef _WIN32 */
 
 static PyObject *listdir(PyObject *self, PyObject *args, PyObject *kwargs)
@@ -1291,6 +1311,8 @@
 	{"getfstype", (PyCFunction)getfstype, METH_VARARGS,
 	 "get filesystem type (best-effort)\n"},
 #endif
+	{"unblocksignal", (PyCFunction)unblocksignal, METH_VARARGS,
+	 "change signal mask to unblock a given signal\n"},
 #endif /* ndef _WIN32 */
 #ifdef __APPLE__
 	{
@@ -1301,7 +1323,7 @@
 	{NULL, NULL}
 };
 
-static const int version = 1;
+static const int version = 2;
 
 #ifdef IS_PY3K
 static struct PyModuleDef osutil_module = {
diff --git a/mercurial/policy.py b/mercurial/policy.py
--- a/mercurial/policy.py
+++ b/mercurial/policy.py
@@ -74,7 +74,7 @@
     (r'cext', r'bdiff'): 1,
     (r'cext', r'diffhelpers'): 1,
     (r'cext', r'mpatch'): 1,
-    (r'cext', r'osutil'): 1,
+    (r'cext', r'osutil'): 2,
     (r'cext', r'parsers'): 4,
 }
 
diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -163,6 +163,10 @@
     setprocname = osutil.setprocname
 except AttributeError:
     pass
+try:
+    unblocksignal = osutil.unblocksignal
+except AttributeError:
+    pass
 
 # Python compatibility