diff --git a/lib/wp/spa-json.c b/lib/wp/spa-json.c
index cc76d960..193d1051 100644
--- a/lib/wp/spa-json.c
+++ b/lib/wp/spa-json.c
@@ -170,11 +170,26 @@ wp_spa_json_new (const gchar *data, size_t size)
  */
 WpSpaJson *
 wp_spa_json_new_from_string (const gchar *json_str)
+{
+  return wp_spa_json_new_from_stringn(json_str, strlen (json_str));
+}
+
+/*!
+ * \brief Constructs a new WpSpaJson from a JSON string with specific length.
+ *
+ * \ingroup wpspajson
+ * \param json_str a JSON string
+ * \param len the specific length of the string
+ * \returns a new WpSpaJson that references the data in \a json_str. \a json_str
+ *   is not copied, so it needs to stay alive.
+ */
+WpSpaJson *
+wp_spa_json_new_from_stringn (const gchar *json_str, size_t len)
 {
   WpSpaJson *self = g_slice_new0 (WpSpaJson);
   g_ref_count_init (&self->ref);
   self->flags = FLAG_NO_OWNERSHIP;
-  spa_json_init (&self->json_data, json_str, strlen (json_str));
+  spa_json_init (&self->json_data, json_str, len);
   self->builder = NULL;
   self->data = (gchar *)self->json_data.cur;
   self->size = self->json_data.end - self->json_data.cur;
diff --git a/lib/wp/spa-json.h b/lib/wp/spa-json.h
index 085ce5e6..1e51b220 100644
--- a/lib/wp/spa-json.h
+++ b/lib/wp/spa-json.h
@@ -37,6 +37,9 @@ void wp_spa_json_unref (WpSpaJson *self);
 WP_API
 WpSpaJson * wp_spa_json_new_from_string (const gchar *json_str);
 
+WP_API
+WpSpaJson * wp_spa_json_new_from_stringn (const gchar *json_str, size_t len);
+
 WP_API
 WpSpaJson * wp_spa_json_new_wrap (struct spa_json *json);