diff --git a/src/main/java/de/ids_mannheim/korap/query/serialize/PoliqarpPlusTree.java b/src/main/java/de/ids_mannheim/korap/query/serialize/PoliqarpPlusTree.java
index 5418c09..397ee5f 100644
--- a/src/main/java/de/ids_mannheim/korap/query/serialize/PoliqarpPlusTree.java
+++ b/src/main/java/de/ids_mannheim/korap/query/serialize/PoliqarpPlusTree.java
@@ -298,7 +298,7 @@
 
 		if (nodeCat.equals("spanclass")) {
 			// Step I: get info
-			int classId = 0;
+			int classId = 1;
 			if (getNodeCat(node.getChild(1)).equals("spanclass_id")) {
 				String ref = node.getChild(1).getChild(0).toStringTree(parser);
 				try {
@@ -311,7 +311,7 @@
 				}
 				// only allow class id up to 255
 				if (classId > 255) {
-					classId = 0;
+					classId = 1;
 				}
 			}
 			LinkedHashMap<String, Object> classGroup = makeSpanClass(classId, false);
@@ -343,7 +343,7 @@
 					}
 				}
 			} else {
-				classRefs.add(0);
+				classRefs.add(1);
 			}
 			LinkedHashMap<String, Object> referenceGroup = makeReference(classRefs);
 
diff --git a/src/test/java/PoliqarpPlusTreeTest.java b/src/test/java/PoliqarpPlusTreeTest.java
index 27e4fca..3f87c21 100644
--- a/src/test/java/PoliqarpPlusTreeTest.java
+++ b/src/test/java/PoliqarpPlusTreeTest.java
@@ -873,7 +873,7 @@
 	public void testClasses() throws QueryException {
 		String query;
 		// {[base=Mann]}
-		String cls1 = "{@type=korap:group, operation=operation:class, class=0, classOut=0, operands=[" +
+		String cls1 = "{@type=korap:group, operation=operation:class, class=1, classOut=1, operands=[" +
 				"{@type=korap:token, wrap={@type=korap:term, layer=lemma, key=Mann, match=match:eq}}" +
 				"]}";
 		ppt = new PoliqarpPlusTree("{[base=Mann]}");
@@ -882,7 +882,7 @@
 		
 		// {[base=Mann][orth=Frau]}
 		query = "{[base=Mann][orth=Frau]}";
-		String cls2 = "{@type=korap:group, operation=operation:class, class=0, classOut=0, operands=[" +
+		String cls2 = "{@type=korap:group, operation=operation:class, class=1, classOut=1, operands=[" +
 				 "{@type=korap:group, operation=operation:sequence, operands=[" +
 				  "{@type=korap:token, wrap={@type=korap:term, layer=lemma, key=Mann, match=match:eq}}," +
 				  "{@type=korap:token, wrap={@type=korap:term, layer=orth, key=Frau, match=match:eq}}" +
@@ -895,7 +895,7 @@
 		// [p=NN]{[base=Mann][orth=Frau]}
 		String cls3 = "{@type=korap:group, operation=operation:sequence, operands=[" +
 						"{@type=korap:token, wrap={@type=korap:term, layer=p, key=NN, match=match:eq}}," +
-						"{@type=korap:group, operation=operation:class, class=0, classOut=0, operands=[" +
+						"{@type=korap:group, operation=operation:class, class=1, classOut=1, operands=[" +
 							"{@type=korap:group, operation=operation:sequence, operands=[" +
 								"{@type=korap:token, wrap={@type=korap:term, layer=lemma, key=Mann, match=match:eq}}," +
 								"{@type=korap:token, wrap={@type=korap:term, layer=orth, key=Frau, match=match:eq}}" +
@@ -908,7 +908,7 @@
 		
 		// {[base=Mann][orth=Frau]}[p=NN]
 		String cls4 = "{@type=korap:group, operation=operation:sequence, operands=[" +
-						"{@type=korap:group, operation=operation:class, class=0, classOut=0, operands=[" +
+						"{@type=korap:group, operation=operation:class, class=1, classOut=1, operands=[" +
 						   "{@type=korap:group, operation=operation:sequence, operands=[" +
 						     "{@type=korap:token, wrap={@type=korap:term, layer=lemma, key=Mann, match=match:eq}}," +
 						     "{@type=korap:token, wrap={@type=korap:term, layer=orth, key=Frau, match=match:eq}}" +
@@ -1025,10 +1025,10 @@
 	public void testFocusSplit() throws QueryException {
 		// focus([orth=Der]{[orth=Mann]})
 		String shr1 = 
-			"{@type=korap:reference, operation=operation:focus, classRef=[0], operands=[" +
+			"{@type=korap:reference, operation=operation:focus, classRef=[1], operands=[" +
 				"{@type=korap:group, operation=operation:sequence, operands=[" +
 					"{@type=korap:token, wrap={@type=korap:term, layer=orth, key=Der, match=match:eq}}," +
-					"{@type=korap:group, operation=operation:class, class=0, classOut=0, operands=[" +
+					"{@type=korap:group, operation=operation:class, class=1, classOut=1, operands=[" +
 						"{@type=korap:token, wrap={@type=korap:term, layer=orth, key=Mann, match=match:eq}}" +
 					"]}" +
 				"]}" +
@@ -1039,10 +1039,10 @@
 		
 		// focus([orth=Der]{[orth=Mann][orth=geht]})
 		String shr2 = 
-			"{@type=korap:reference, operation=operation:focus, classRef=[0], operands=[" +
+			"{@type=korap:reference, operation=operation:focus, classRef=[1], operands=[" +
 				"{@type=korap:group, operation=operation:sequence, operands=[" +
 					"{@type=korap:token, wrap={@type=korap:term, layer=orth, key=Der, match=match:eq}}," +
-					"{@type=korap:group, operation=operation:class, class=0, classOut=0, operands=[" +
+					"{@type=korap:group, operation=operation:class, class=1, classOut=1, operands=[" +
 						"{@type=korap:group, operation=operation:sequence, operands=[" +
 							"{@type=korap:token, wrap={@type=korap:term, layer=orth, key=Mann, match=match:eq}}," +
 							"{@type=korap:token, wrap={@type=korap:term, layer=orth, key=geht, match=match:eq}}" +
@@ -1161,7 +1161,7 @@
 		String shr8 = 
 			"{@type=korap:reference, operation=operation:focus, classRef=[1], operands=[" +
 				"{@type=korap:group, operation=operation:sequence, operands=[" +
-					"{@type=korap:group, operation=operation:class, class=0, classOut=0, operands=[" +
+					"{@type=korap:group, operation=operation:class, class=1, classOut=1, operands=[" +
 						"{@type=korap:token, wrap={@type=korap:term, layer=lemma, key=der, match=match:eq}}" +
 					"]}," +
 					"{@type=korap:group, operation=operation:class, class=1, classOut=1, operands=[" +