diff --git a/CityDoctorParent/CityDoctorModel/src/main/java/de/hft/stuttgart/citydoctor2/zip/CityGmlZipInputStream.java b/CityDoctorParent/CityDoctorModel/src/main/java/de/hft/stuttgart/citydoctor2/zip/CityGmlZipInputStream.java
index 593f3648a7d952862a922b1462cb24d3b7def2da..1491ebff0e3e82816e44b5d75750cce57a324cbd 100644
--- a/CityDoctorParent/CityDoctorModel/src/main/java/de/hft/stuttgart/citydoctor2/zip/CityGmlZipInputStream.java
+++ b/CityDoctorParent/CityDoctorModel/src/main/java/de/hft/stuttgart/citydoctor2/zip/CityGmlZipInputStream.java
@@ -8,8 +8,8 @@ import java.util.zip.ZipFile;
 
 public class CityGmlZipInputStream implements AutoCloseable {
 
-    private ZipFile zip;
-    private ZipEntry zipEntry;
+    private final ZipFile zip;
+    private final ZipEntry zipEntry;
     private boolean closed = false;
     private static final long MB = 1024 * 1024L;