diff --git a/ext/libxml/libxml.c b/ext/libxml/libxml.c
index 33c2a6f2aed..ece46c438bf 100644
--- a/ext/libxml/libxml.c
+++ b/ext/libxml/libxml.c
@@ -932,11 +932,13 @@ PHP_LIBXML_API void php_libxml_initialize(void)
 		ZEND_IGNORE_LEAKS_BEGIN();
 
 		xmlInitParser();
-#ifdef LIBXML_SCHEMAS_ENABLED
+#ifdef ZTS
+# ifdef LIBXML_SCHEMAS_ENABLED
 		xmlSchemaInitTypes();
-#endif
-#ifdef LIBXML_RELAXNG_ENABLED
+# endif
+# ifdef LIBXML_RELAXNG_ENABLED
 		xmlRelaxNGInitTypes();
+# endif
 #endif
 		ZEND_IGNORE_LEAKS_END();