diff --git a/VERSION b/VERSION
index b3d91f9c..450ad1e2 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-5.9.0
+5.9.1
diff --git a/gortools/src/main/scala/gorsat/Utilities/IteratorUtilities.scala b/gortools/src/main/scala/gorsat/Utilities/IteratorUtilities.scala
index df3a9877..79350286 100644
--- a/gortools/src/main/scala/gorsat/Utilities/IteratorUtilities.scala
+++ b/gortools/src/main/scala/gorsat/Utilities/IteratorUtilities.scala
@@ -43,7 +43,7 @@ object IteratorUtilities {
 
   private val logger = LoggerFactory.getLogger(this.getClass)
 
-  private val ALLOW_DUPLICATE_COLUMNS = System.getProperty("gor.iterators.allowDuplicateColumns", "true").toBoolean
+  private val ALLOW_DUPLICATE_COLUMNS = System.getProperty("gor.iterators.allowDuplicateColumns", "false").toBoolean
 
   def getHeader(filename: String, gorRoot: String, context: GorContext): String = {
     val gm: GorMonitor = null