diff --git a/core/modules/rdf/rdf.api.php b/core/modules/rdf/rdf.api.php
index 7a9e38ec3809..3dbe7d1e2677 100644
--- a/core/modules/rdf/rdf.api.php
+++ b/core/modules/rdf/rdf.api.php
@@ -18,7 +18,7 @@
  * defined in rdf_rdf_namespaces(), this hook should be used to define the new
  * namespace prefixes.
  *
- * @return
+ * @return string[]
  *   An associative array of namespaces where the key is the namespace prefix
  *   and the value is the namespace URI.
  *