diff --git a/src/calibre/utils/lzx/lzxmodule.c b/src/calibre/utils/lzx/lzxmodule.c
index a1917b5749..c45bb22c95 100644
--- a/src/calibre/utils/lzx/lzxmodule.c
+++ b/src/calibre/utils/lzx/lzxmodule.c
@@ -187,6 +187,7 @@ decompress(PyObject *self, PyObject *args)
 
     if (err != MSPACK_ERR_OK) {
         Py_DECREF(retval);
+        retval = NULL;
         PyErr_SetString(LzxError, "LZX decompression failed");
     }