diff --git a/schematron.c b/schematron.c
index dbf4543..dfc9a65 100644
--- a/schematron.c
+++ b/schematron.c
@@ -470,7 +470,7 @@
     ret->type = XML_STRON_CTXT_PARSER;
     ret->dict = xmlDictCreate();
     ret->URL = xmlDictLookup(ret->dict, (const xmlChar *) URL, -1);
-    ret->includes = 0;
+    ret->includes = NULL;
     ret->xctxt = xmlXPathNewContext(NULL);
     if (ret->xctxt == NULL) {
         xmlSchematronPErrMemory(NULL, "allocating schema parser XPath context",