diff --git a/src/main/java/de/marhali/easyi18n/io/parser/properties/SortableProperties.java b/src/main/java/de/marhali/easyi18n/io/parser/properties/SortableProperties.java
index 7d21bb1..f4bc3be 100644
--- a/src/main/java/de/marhali/easyi18n/io/parser/properties/SortableProperties.java
+++ b/src/main/java/de/marhali/easyi18n/io/parser/properties/SortableProperties.java
@@ -39,7 +39,7 @@ public class SortableProperties extends Properties {
     }
 
     @Override
-    public String toString() {
+    public synchronized String toString() {
         return this.properties.toString();
     }
 }
\ No newline at end of file