diff --git a/tools/BUILD b/tools/BUILD
index ce15280e..3df7f55 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -47,7 +47,7 @@
         "-Xep:FutureReturnValueIgnored:ERROR",
         "-Xep:GetClassOnEnum:ERROR",
         "-Xep:ImmutableAnnotationChecker:ERROR",
-        "-Xep:ImmutableEnumChecker:WARN",
+        "-Xep:ImmutableEnumChecker:ERROR",
         "-Xep:IncompatibleModifiers:ERROR",
         "-Xep:InjectOnConstructorOfAbstractClass:ERROR",
         "-Xep:InputStreamSlowMultibyteRead:ERROR",