+#ifdef FEATURE_EXTERNAL_FILTERS
+extern privoxy_mutex_t external_filter_mutex;
+#endif
+
+#ifndef HAVE_GMTIME_R
+extern privoxy_mutex_t gmtime_mutex;
+#endif /* ndef HAVE_GMTIME_R */
+
+#ifndef HAVE_LOCALTIME_R
+extern privoxy_mutex_t localtime_mutex;
+#endif /* ndef HAVE_GMTIME_R */