diff --git a/src/main/groovy/org/ajoberstar/grgit/Repository.groovy b/src/main/groovy/org/ajoberstar/grgit/Repository.groovy
index dcfa8359..29e22101 100644
--- a/src/main/groovy/org/ajoberstar/grgit/Repository.groovy
+++ b/src/main/groovy/org/ajoberstar/grgit/Repository.groovy
@@ -23,7 +23,7 @@ import org.eclipse.jgit.api.Git
  * A repository.
  * @since 0.1.0
  */
-@Immutable(knownImmutableClasses=[Git, File])
+@Immutable(knownImmutableClasses=[Git, File, Credentials])
 class Repository {
   /**
    * The directory the repository is contained in.