diff --git a/src/main/kotlin/com/github/jengelman/gradle/plugins/shadow/ShadowDsl.kt b/src/main/kotlin/com/github/jengelman/gradle/plugins/shadow/ShadowDsl.kt
index fea611e3d..099ffc8cf 100644
--- a/src/main/kotlin/com/github/jengelman/gradle/plugins/shadow/ShadowDsl.kt
+++ b/src/main/kotlin/com/github/jengelman/gradle/plugins/shadow/ShadowDsl.kt
@@ -6,6 +6,7 @@ package com.github.jengelman.gradle.plugins.shadow
 @Deprecated(
   message = "Use `ShadowDsl` instead. This will be removed in Shadow 10.",
   replaceWith = ReplaceWith("ShadowDsl", "com.github.jengelman.gradle.plugins.shadow.ShadowDsl"),
+  level = DeprecationLevel.ERROR,
 )
 @DslMarker
 public annotation class ShadowDslMarker