diff --git a/BimServer/src/org/bimserver/geometry/GeometryGenerationReport.java b/BimServer/src/org/bimserver/geometry/GeometryGenerationReport.java
index <HASH>..<HASH> 100644
--- a/BimServer/src/org/bimserver/geometry/GeometryGenerationReport.java
+++ b/BimServer/src/org/bimserver/geometry/GeometryGenerationReport.java
@@ -26,7 +26,7 @@ import java.util.HashMap;
 import java.util.LinkedHashSet;
 import java.util.Map;
 import java.util.Set;
-import java.util.TreeMap;
+import java.util.concurrent.ConcurrentSkipListMap;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import org.bimserver.emf.Schema;
@@ -59,7 +59,7 @@ public class GeometryGenerationReport {
 	private int numberOfTriangles;

 	private int numberOfTrianglesIncludingReuse;

 	private boolean reuseGeometry;

-	private Map<Integer, String> debugFiles = new TreeMap<>();

+	private final Map<Integer, String> debugFiles = new ConcurrentSkipListMap<>();

 	

 	public synchronized void incrementTriangles(int triangles) {

 		this.numberOfTriangles += triangles;
Fixed concurrency issue when writing debug files (endless loop...)