diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/deprecation/DeprecationInfoAction.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/deprecation/DeprecationInfoAction.java
index c4f89bafbf8ba..d32ed514a47a6 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/deprecation/DeprecationInfoAction.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/deprecation/DeprecationInfoAction.java
@@ -131,7 +131,7 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
                 .array("node_settings", nodeSettingsIssues.toArray())
                 .field("index_settings")
                     .map(indexSettingsIssues)
-                .array("ml_settings", mlSettingsIssues)
+                .array("ml_settings", mlSettingsIssues.toArray())
                 .endObject();
         }