diff --git a/apps/emqx/src/emqx_schema.erl b/apps/emqx/src/emqx_schema.erl
index a80be2424..2d71a1d69 100644
--- a/apps/emqx/src/emqx_schema.erl
+++ b/apps/emqx/src/emqx_schema.erl
@@ -331,10 +331,7 @@ fields("mqtt") ->
     ];
 
 fields("zone") ->
-    Fields = ["mqtt", "stats", "flapping_detect", "force_shutdown",
-              "conn_congestion", "rate_limit", "quota", "force_gc",
-              "overload_protection"
-             ],
+    Fields = emqx_zone_schema:roots(),
     [{F, ref(emqx_zone_schema, F)} || F <- Fields];
 
 fields("rate_limit") ->
diff --git a/apps/emqx/src/emqx_zone_schema.erl b/apps/emqx/src/emqx_zone_schema.erl
index 013ffb22f..1d24f9481 100644
--- a/apps/emqx/src/emqx_zone_schema.erl
+++ b/apps/emqx/src/emqx_zone_schema.erl
@@ -20,7 +20,12 @@
 
 namespace() -> zone.
 
-roots() -> [].
+%% this shcema module is not used at root level.
+%% roots are added only for document generation.
+roots() -> ["mqtt", "stats", "flapping_detect", "force_shutdown",
+            "conn_congestion", "rate_limit", "quota", "force_gc",
+            "overload_protection"
+           ].
 
 %% zone schemas are clones from the same name from root level
 %% only not allowed to have default values.