diff --git a/http.c b/http.c
index e9dc877..6f4bab0 100644
--- a/http.c
+++ b/http.c
@@ -313,6 +313,28 @@ http_strtolower(const char *input)
 }
 
 
+#if PG_VERSION_NUM < 160000
+static char *
+guc_strdup(int elevel, const char *src)
+{
+    char       *data;
+
+    data = pstrdup(src);
+    if (data == NULL)
+        ereport(elevel,
+                (errcode(ERRCODE_OUT_OF_MEMORY),
+                 errmsg("out of memory")));
+    return data;
+}
+
+static void
+guc_free(void *ptr)
+{
+	pfree(ptr);
+}
+#endif
+
+
 static void
 http_guc_init_opt(http_curlopt *opt)
 {