diff --git a/src/main/java/org/apache/maven/plugins/resources/ResourcesMojo.java b/src/main/java/org/apache/maven/plugins/resources/ResourcesMojo.java
index e622efc..a622653 100644
--- a/src/main/java/org/apache/maven/plugins/resources/ResourcesMojo.java
+++ b/src/main/java/org/apache/maven/plugins/resources/ResourcesMojo.java
@@ -77,7 +77,7 @@ public class ResourcesMojo extends AbstractMojo {
     /**
      * The list of resources we want to transfer.
      */
-    @Parameter(defaultValue = "${project.resources}", required = true)
+    @Parameter(defaultValue = "${project.resources}", required = true, readonly = true)
     private List<Resource> resources;
 
     /**