diff --git a/src/python/core.c b/src/python/core.c
index 4b1ab89f..79f6018b 100644
--- a/src/python/core.c
+++ b/src/python/core.c
@@ -21,6 +21,7 @@
 static PyObject *
 mkcache_bytes(PyObject *self, PyObject *args) {
     unsigned long block_number;
+    unsigned long cache_size;
 
     if (!PyArg_ParseTuple(args, "k", &block_number))
         return 0;