Fix double decref.
diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index 1066702..e0da011 100644
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -559,7 +559,6 @@
 
 error:
 	Py_DECREF(result);
-	Py_XDECREF(iobj);
 	return NULL;
 }