diff --git a/Modules/cStringIO.c b/Modules/cStringIO.c
index 0b4faa3..385999f 100644
--- a/Modules/cStringIO.c
+++ b/Modules/cStringIO.c
@@ -173,7 +173,7 @@
 static PyObject *
 IO_read(IOobject *self, PyObject *args) {
         Py_ssize_t n = -1;
-        char *output;
+        char *output = NULL;
 
         UNLESS (PyArg_ParseTuple(args, "|n:read", &n)) return NULL;