make read-only parameter read-only
diff --git a/src/main/java/org/apache/maven/plugins/wrapper/WrapperMojo.java b/src/main/java/org/apache/maven/plugins/wrapper/WrapperMojo.java
index a9ae2ae..40b0cd6 100644
--- a/src/main/java/org/apache/maven/plugins/wrapper/WrapperMojo.java
+++ b/src/main/java/org/apache/maven/plugins/wrapper/WrapperMojo.java
@@ -95,7 +95,7 @@
     private MavenSession session;
     
     // Waiting for org.codehaus.plexus.component.configurator.converters.basic.PathConverter
-    @Parameter( defaultValue = "${project.basedir}" )
+    @Parameter( defaultValue = "${project.basedir}", readonly = true, required = true )
     private File basedir;
 
     // CONSTANTS