From 4b9b936429c8d013b0e954d0a4d30832e6354439 Mon Sep 17 00:00:00 2001
From: Nick Coghlan <ncoghlan@gmail.com>
Date: Sat, 16 Nov 2013 00:34:13 +1000
Subject: [PATCH] Don't decref exc too soon

---
 Objects/exceptions.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index bb61ea5a3c6..3476db02dfc 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -2685,7 +2685,6 @@ _PyErr_TrySetFromCause(const char *format, ...)
      * state potentially stored on OSError instances.
      */
 
-    Py_DECREF(exc);
     Py_XDECREF(tb);
 
 #ifdef HAVE_STDARG_PROTOTYPES
@@ -2696,12 +2695,14 @@ _PyErr_TrySetFromCause(const char *format, ...)
     msg_prefix = PyUnicode_FromFormatV(format, vargs);
     va_end(vargs);
     if (msg_prefix == NULL) {
+        Py_DECREF(exc);
         Py_DECREF(val);
         return NULL;
     }
 
     PyErr_Format(exc, "%U (%s: %S)",
                  msg_prefix, Py_TYPE(val)->tp_name, val);
+    Py_DECREF(exc);
     Py_DECREF(msg_prefix);
     PyErr_Fetch(&new_exc, &new_val, &new_tb);
     PyErr_NormalizeException(&new_exc, &new_val, &new_tb);