diff --git a/src/main/java/de/ids_mannheim/korap/query/spans/FocusSpans.java b/src/main/java/de/ids_mannheim/korap/query/spans/FocusSpans.java
index 244c79d..873aaf2 100644
--- a/src/main/java/de/ids_mannheim/korap/query/spans/FocusSpans.java
+++ b/src/main/java/de/ids_mannheim/korap/query/spans/FocusSpans.java
@@ -3,10 +3,10 @@
 import static de.ids_mannheim.korap.util.KrillByte.byte2int;
 
 import java.io.IOException;
-import java.util.ArrayList;
-import java.util.Collections;
+import java.util.Comparator;
 import java.util.List;
 import java.util.Map;
+import java.util.PriorityQueue;
 
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.Term;
@@ -53,10 +53,13 @@
     public static final boolean DEBUG = false;
 
     private boolean isSorted, matchTemporaryClass, removeTemporaryClasses;
-    private List<CandidateSpan> candidateSpans;
+    // private List<CandidateSpan> candidateSpans;
     private int windowSize = 10;
     private int currentDoc;
-
+    private int prevStart;
+    private int prevDoc;
+    private PriorityQueue<CandidateSpan> candidates;
+    private FocusSpanComparator comparator;
 
     /**
      * Construct a FocusSpan for the given {@link SpanQuery}.
@@ -86,7 +89,8 @@
         isSorted = query.isSorted();
         matchTemporaryClass = query.matchTemporaryClass();
         removeTemporaryClasses = query.removeTemporaryClasses();
-        candidateSpans = new ArrayList<CandidateSpan>();
+        // candidateSpans = new ArrayList<CandidateSpan>();
+        candidates = new PriorityQueue<>(windowSize, comparator);
         hasMoreSpans = firstSpans.next();
         currentDoc = firstSpans.doc();
 
@@ -99,7 +103,7 @@
         matchPayload.clear();
         spanId = 0;
         CandidateSpan cs;
-        while (hasMoreSpans || candidateSpans.size() > 0) {
+        while (hasMoreSpans || candidates.size() > 0) {
             if (isSorted) {
 
                 if (firstSpans.isPayloadAvailable()
@@ -111,14 +115,13 @@
                 }
                 hasMoreSpans = firstSpans.next();
             }
-            else if (candidateSpans.isEmpty()) {
+            else if (candidates.isEmpty()) {
                 currentDoc = firstSpans.doc();
                 collectCandidates();
-                Collections.sort(candidateSpans);
             }
             else {
-                setMatch(candidateSpans.get(0));
-                candidateSpans.remove(0);
+                setMatch(candidates.poll());
+                collectCandidates();
                 return true;
             }
         }
@@ -129,22 +132,29 @@
 
     private void collectCandidates () throws IOException {
         CandidateSpan cs = null;
-        while (hasMoreSpans && candidateSpans.size() < windowSize
+        while (hasMoreSpans && candidates.size() < windowSize
                 && firstSpans.doc() == currentDoc) {
 
             if (firstSpans.isPayloadAvailable()
                     && updateSpanPositions(cs = new CandidateSpan(firstSpans))) {
-                candidateSpans.add(cs);
+                if (cs.getDoc() == prevDoc && cs.getStart() < prevStart) {
+                    log.warn("Span (" + cs.getStart() + ", "
+                            + cs.getEnd() + ") is out of order and skipped.");
+                }
+                else {
+                    candidates.add(cs);
+                }
             }
             hasMoreSpans = firstSpans.next();
         }
     }
 
-
     private void setMatch (CandidateSpan cs) {
         matchStartPosition = cs.getStart();
+        prevStart = matchStartPosition;
         matchEndPosition = cs.getEnd();
         matchDocNumber = cs.getDoc();
+        prevDoc = matchDocNumber;
         matchPayload.addAll(cs.getPayloads());
 
         if (firstSpans instanceof RelationSpans && classNumbers.size() == 1) {
@@ -244,7 +254,18 @@
     // Todo: Check for this on document boundaries!
     @Override
     public boolean skipTo (int target) throws IOException {
-        if (this.doc() < target && firstSpans.skipTo(target)) {
+        if (candidates.size() > 0) {
+            CandidateSpan cs;
+            while ((cs = candidates.poll()) != null) {
+                if (cs.getDoc() == target) {
+                    return next();
+                }
+            }
+        }
+        if (firstSpans.doc() == target) {
+            return next();
+        }
+        if (firstSpans.doc() < target && firstSpans.skipTo(target)) {
             return next();
         }
         return false;
@@ -262,4 +283,28 @@
     public long cost () {
         return firstSpans.cost();
     };
+    
+    class FocusSpanComparator implements Comparator<CandidateSpan> {
+
+        @Override
+        public int compare(CandidateSpan o1, CandidateSpan o2) {
+            if (o1.doc == o2.doc) {
+                if (o1.getStart() == o2.getStart()) {
+                    if (o1.getEnd() == o2.getEnd()) return 0;
+                    if (o1.getEnd() > o2.getEnd())
+                        return 1;
+                    else
+                        return -1;
+                }
+                else if (o1.getStart() < o2.getStart())
+                    return -1;
+                else
+                    return 1;
+            }
+            else if (o1.doc < o2.doc)
+                return -1;
+            else
+                return 1;
+        }
+    }
 };
diff --git a/src/test/java/de/ids_mannheim/korap/index/TestFocusIndex.java b/src/test/java/de/ids_mannheim/korap/index/TestFocusIndex.java
new file mode 100644
index 0000000..2f668e2
--- /dev/null
+++ b/src/test/java/de/ids_mannheim/korap/index/TestFocusIndex.java
@@ -0,0 +1,46 @@
+package de.ids_mannheim.korap.index;
+
+import java.io.IOException;
+
+import org.apache.lucene.index.Term;
+import org.apache.lucene.search.spans.SpanTermQuery;
+import org.junit.Test;
+
+import de.ids_mannheim.korap.KrillIndex;
+import de.ids_mannheim.korap.query.SpanFocusQuery;
+import de.ids_mannheim.korap.query.SpanNextQuery;
+import de.ids_mannheim.korap.query.SpanRelationQuery;
+import de.ids_mannheim.korap.response.Match;
+import de.ids_mannheim.korap.response.Result;
+
+public class TestFocusIndex {
+    private KrillIndex ki;
+    private Result kr;
+
+    public TestFocusIndex () throws IOException {
+        ki = new KrillIndex();
+    }
+
+    /**
+     * Check Skipto focus spans
+     * */
+    @Test
+    public void testCase12() throws IOException {
+        ki.addDoc(TestRelationIndex.createFieldDoc0());
+        ki.addDoc(TestRelationIndex.createFieldDoc1());
+        ki.commit();
+        SpanRelationQuery sq = new SpanRelationQuery(new SpanTermQuery(
+                new Term("base", ">:xip/syntax-dep_rel")), true);
+        sq.setSourceClass((byte) 1);
+
+        SpanFocusQuery sfq = new SpanFocusQuery(sq, (byte) 1);
+        sfq.setSorted(false);
+        SpanTermQuery stq = new SpanTermQuery(new Term("base", "s:c"));
+        SpanNextQuery snq = new SpanNextQuery(stq, sfq);
+
+        kr = ki.search(snq, (short) 20);
+        for (Match m : kr.getMatches()) {
+            System.out.println(m.getStartPos() + " " + m.getEndPos());
+        }
+    }
+}
diff --git a/src/test/java/de/ids_mannheim/korap/index/TestNextIndex.java b/src/test/java/de/ids_mannheim/korap/index/TestNextIndex.java
index 23674b6..0465585 100644
--- a/src/test/java/de/ids_mannheim/korap/index/TestNextIndex.java
+++ b/src/test/java/de/ids_mannheim/korap/index/TestNextIndex.java
@@ -13,9 +13,12 @@
 import org.junit.runners.JUnit4;
 
 import de.ids_mannheim.korap.KrillIndex;
+import de.ids_mannheim.korap.query.SpanClassQuery;
 import de.ids_mannheim.korap.query.SpanElementQuery;
+import de.ids_mannheim.korap.query.SpanFocusQuery;
 import de.ids_mannheim.korap.query.SpanNextQuery;
 import de.ids_mannheim.korap.query.wrap.SpanSequenceQueryWrapper;
+import de.ids_mannheim.korap.response.Match;
 import de.ids_mannheim.korap.response.Result;
 
 @RunWith(JUnit4.class)
@@ -262,6 +265,23 @@
         assertEquals("StartPos", 0, kr.getMatch(0).startPos);
         assertEquals("EndPos", 3, kr.getMatch(0).endPos);
 
+        sq = new SpanNextQuery(new SpanTermQuery(new Term("base", "s:c")),
+                new SpanNextQuery(new SpanFocusQuery(new SpanClassQuery(
+                        new SpanTermQuery(new Term("base", "s:d")), (byte) 1),
+                        (byte) 1), new SpanFocusQuery(new SpanClassQuery(
+                        new SpanTermQuery(new Term("base", "s:b")), (byte) 2),
+                        (byte) 2)));
+
+        kr = ki.search(sq, (short) 10);
+        assertEquals("doc-number", 2, kr.getMatch(0).getLocalDocID());
+        assertEquals("StartPos", 0, kr.getMatch(0).startPos);
+        assertEquals("EndPos", 3, kr.getMatch(0).endPos);
+
+        // for (Match km : kr.getMatches()) {
+        // System.out.println(km.getStartPos() + "," + km.getEndPos()
+        // + " "
+        // + km.getSnippetBrackets());
+        // }
     }
 
 
diff --git a/src/test/java/de/ids_mannheim/korap/index/TestRelationIndex.java b/src/test/java/de/ids_mannheim/korap/index/TestRelationIndex.java
index d8f79a7..7df32ea 100644
--- a/src/test/java/de/ids_mannheim/korap/index/TestRelationIndex.java
+++ b/src/test/java/de/ids_mannheim/korap/index/TestRelationIndex.java
@@ -14,6 +14,7 @@
 import de.ids_mannheim.korap.query.SpanClassQuery;
 import de.ids_mannheim.korap.query.SpanElementQuery;
 import de.ids_mannheim.korap.query.SpanFocusQuery;
+import de.ids_mannheim.korap.query.SpanNextQuery;
 import de.ids_mannheim.korap.query.SpanRelationMatchQuery;
 import de.ids_mannheim.korap.query.SpanRelationQuery;
 import de.ids_mannheim.korap.query.SpanSegmentQuery;
@@ -71,7 +72,7 @@
     }
 
 
-    private FieldDocument createFieldDoc0 () {
+    public static FieldDocument createFieldDoc0() {
         FieldDocument fd = new FieldDocument();
         fd.addString("ID", "doc-0");
         fd.addTV(
@@ -96,7 +97,7 @@
     }
 
 
-    private FieldDocument createFieldDoc1 () {
+    public static FieldDocument createFieldDoc1() {
         FieldDocument fd = new FieldDocument();
         fd.addString("ID", "doc-1");
         fd.addTV(
@@ -903,9 +904,6 @@
         assertEquals((long) 1, kr.getTotalResults());
         assertEquals(2, kr.getMatch(0).getStartPos());
         assertEquals(7, kr.getMatch(0).getEndPos());
-
-        // for (Match m : kr.getMatches()) {
-        // System.out.println(m.getStartPos() + " " + m.getEndPos());
-        // }
     }
+
 }