diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 71a715b80f3..b6d0bb3d973 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -155,6 +155,13 @@ Tests
   expression to encapsulate a statement that is expected to throw an exception.
   (Ryan Ernst)
 
+Bug Fixes
+
+* LUCENE-7065: Fix the explain for the global ordinals join query. Before the
+  explain would also indicate that non matching documents would match.
+  On top of that with score mode average, the explain would fail with a NPE.
+  (Martijn van Groningen)
+
 Other
 
 * LUCENE-7035: Upgrade icu4j to 56.1/unicode 8. (Robert Muir)
diff --git a/lucene/join/src/java/org/apache/lucene/search/join/GlobalOrdinalsQuery.java b/lucene/join/src/java/org/apache/lucene/search/join/GlobalOrdinalsQuery.java
index 5bd8c4c8368..f9b74d46932 100644
--- a/lucene/join/src/java/org/apache/lucene/search/join/GlobalOrdinalsQuery.java
+++ b/lucene/join/src/java/org/apache/lucene/search/join/GlobalOrdinalsQuery.java
@@ -112,14 +112,27 @@ final class GlobalOrdinalsQuery extends Query {
     @Override
     public Explanation explain(LeafReaderContext context, int doc) throws IOException {
       SortedDocValues values = DocValues.getSorted(context.reader(), joinField);
-      if (values != null) {
-        int segmentOrd = values.getOrd(doc);
-        if (segmentOrd != -1) {
-          BytesRef joinValue = values.lookupOrd(segmentOrd);
-          return Explanation.match(score(), "Score based on join value " + joinValue.utf8ToString());
-        }
+      if (values == null) {
+        return Explanation.noMatch("Not a match");
       }
-      return Explanation.noMatch("Not a match");
+
+      int segmentOrd = values.getOrd(doc);
+      if (segmentOrd == -1) {
+        return Explanation.noMatch("Not a match");
+      }
+      BytesRef joinValue = values.lookupOrd(segmentOrd);
+
+      int ord;
+      if (globalOrds != null) {
+        ord = (int) globalOrds.getGlobalOrds(context.ord).get(segmentOrd);
+      } else {
+        ord = segmentOrd;
+      }
+      if (foundOrds.get(ord) == false) {
+        return Explanation.noMatch("Not a match, join value " + Term.toString(joinValue));
+      }
+
+      return Explanation.match(score(), "A match, join value " + Term.toString(joinValue));
     }
 
     @Override
diff --git a/lucene/join/src/java/org/apache/lucene/search/join/GlobalOrdinalsWithScoreQuery.java b/lucene/join/src/java/org/apache/lucene/search/join/GlobalOrdinalsWithScoreQuery.java
index a85dfa33fb4..f9b2064c65f 100644
--- a/lucene/join/src/java/org/apache/lucene/search/join/GlobalOrdinalsWithScoreQuery.java
+++ b/lucene/join/src/java/org/apache/lucene/search/join/GlobalOrdinalsWithScoreQuery.java
@@ -120,21 +120,28 @@ final class GlobalOrdinalsWithScoreQuery extends Query {
     @Override
     public Explanation explain(LeafReaderContext context, int doc) throws IOException {
       SortedDocValues values = DocValues.getSorted(context.reader(), joinField);
-      if (values != null) {
-        int segmentOrd = values.getOrd(doc);
-        if (segmentOrd != -1) {
-          final float score;
-          if (globalOrds != null) {
-            long globalOrd = globalOrds.getGlobalOrds(context.ord).get(segmentOrd);
-            score = collector.score((int) globalOrd);
-          } else {
-            score = collector.score(segmentOrd);
-          }
-          BytesRef joinValue = values.lookupOrd(segmentOrd);
-          return Explanation.match(score, "Score based on join value " + joinValue.utf8ToString());
-        }
+      if (values == null) {
+        return Explanation.noMatch("Not a match");
       }
-      return Explanation.noMatch("Not a match");
+
+      int segmentOrd = values.getOrd(doc);
+      if (segmentOrd == -1) {
+        return Explanation.noMatch("Not a match");
+      }
+      BytesRef joinValue = values.lookupOrd(segmentOrd);
+
+      int ord;
+      if (globalOrds != null) {
+        ord = (int) globalOrds.getGlobalOrds(context.ord).get(segmentOrd);
+      } else {
+        ord = segmentOrd;
+      }
+      if (collector.match(ord) == false) {
+        return Explanation.noMatch("Not a match, join value " + Term.toString(joinValue));
+      }
+
+      float score = collector.score(ord);
+      return Explanation.match(score, "A match, join value " + Term.toString(joinValue));
     }
 
     @Override
diff --git a/lucene/join/src/test/org/apache/lucene/search/join/TestJoinUtil.java b/lucene/join/src/test/org/apache/lucene/search/join/TestJoinUtil.java
index 9ab886bc54f..af507cdc2fb 100644
--- a/lucene/join/src/test/org/apache/lucene/search/join/TestJoinUtil.java
+++ b/lucene/join/src/test/org/apache/lucene/search/join/TestJoinUtil.java
@@ -48,6 +48,7 @@ import org.apache.lucene.index.BinaryDocValues;
 import org.apache.lucene.index.DirectoryReader;
 import org.apache.lucene.index.DocValues;
 import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.IndexWriter;
 import org.apache.lucene.index.LeafReader;
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.MultiDocValues;
@@ -297,6 +298,108 @@ public class TestJoinUtil extends LuceneTestCase {
     dir.close();
   }
 
+  public void testOrdinalsJoinExplainNoMatches() throws Exception {
+    final String idField = "id";
+    final String productIdField = "productId";
+    // A field indicating to what type a document belongs, which is then used to distinques between documents during joining.
+    final String typeField = "type";
+    // A single sorted doc values field that holds the join values for all document types.
+    // Typically during indexing a schema will automatically create this field with the values
+    final String joinField = idField + productIdField;
+
+    Directory dir = newDirectory();
+    IndexWriter w = new IndexWriter(
+        dir, newIndexWriterConfig(new MockAnalyzer(random())).setMergePolicy(NoMergePolicy.INSTANCE)
+    );
+
+    // 0
+    Document doc = new Document();
+    doc.add(new TextField(idField, "1", Field.Store.NO));
+    doc.add(new TextField(typeField, "product", Field.Store.NO));
+    doc.add(new TextField("description", "random text", Field.Store.NO));
+    doc.add(new TextField("name", "name1", Field.Store.NO));
+    doc.add(new SortedDocValuesField(joinField, new BytesRef("1")));
+    w.addDocument(doc);
+
+    // 1
+    doc = new Document();
+    doc.add(new TextField(idField, "2", Field.Store.NO));
+    doc.add(new TextField(typeField, "product", Field.Store.NO));
+    doc.add(new TextField("description", "random text", Field.Store.NO));
+    doc.add(new TextField("name", "name2", Field.Store.NO));
+    doc.add(new SortedDocValuesField(joinField, new BytesRef("2")));
+    w.addDocument(doc);
+
+    // 2
+    doc = new Document();
+    doc.add(new TextField(productIdField, "1", Field.Store.NO));
+    doc.add(new TextField(typeField, "price", Field.Store.NO));
+    doc.add(new TextField("price", "10.0", Field.Store.NO));
+    doc.add(new SortedDocValuesField(joinField, new BytesRef("1")));
+    w.addDocument(doc);
+
+    // 3
+    doc = new Document();
+    doc.add(new TextField(productIdField, "2", Field.Store.NO));
+    doc.add(new TextField(typeField, "price", Field.Store.NO));
+    doc.add(new TextField("price", "20.0", Field.Store.NO));
+    doc.add(new SortedDocValuesField(joinField, new BytesRef("1")));
+    w.addDocument(doc);
+
+    if (random().nextBoolean()) {
+      w.flush();
+    }
+
+    // 4
+    doc = new Document();
+    doc.add(new TextField(productIdField, "3", Field.Store.NO));
+    doc.add(new TextField(typeField, "price", Field.Store.NO));
+    doc.add(new TextField("price", "5.0", Field.Store.NO));
+    doc.add(new SortedDocValuesField(joinField, new BytesRef("2")));
+    w.addDocument(doc);
+
+    // 5
+    doc = new Document();
+    doc.add(new TextField("field", "value", Field.Store.NO));
+    w.addDocument(doc);
+
+    IndexReader r = DirectoryReader.open(w);
+    IndexSearcher indexSearcher = new IndexSearcher(r);
+    SortedDocValues[] values = new SortedDocValues[r.leaves().size()];
+    for (int i = 0; i < values.length; i++) {
+      LeafReader leafReader =  r.leaves().get(i).reader();
+      values[i] = DocValues.getSorted(leafReader, joinField);
+    }
+    MultiDocValues.OrdinalMap ordinalMap = MultiDocValues.OrdinalMap.build(
+        r.getCoreCacheKey(), values, PackedInts.DEFAULT
+    );
+
+    Query toQuery = new TermQuery(new Term("price", "5.0"));
+    Query fromQuery = new TermQuery(new Term("name", "name2"));
+
+    for (ScoreMode scoreMode : ScoreMode.values()) {
+      Query joinQuery = JoinUtil.createJoinQuery(joinField, fromQuery, toQuery, indexSearcher, scoreMode, ordinalMap);
+      TopDocs result = indexSearcher.search(joinQuery, 10);
+      assertEquals(1, result.totalHits);
+      assertEquals(4, result.scoreDocs[0].doc); // doc with price: 5.0
+      Explanation explanation = indexSearcher.explain(joinQuery, 4);
+      assertTrue(explanation.isMatch());
+      assertEquals(explanation.getDescription(), "A match, join value 2");
+
+      explanation = indexSearcher.explain(joinQuery, 3);
+      assertFalse(explanation.isMatch());
+      assertEquals(explanation.getDescription(), "Not a match, join value 1");
+
+      explanation = indexSearcher.explain(joinQuery, 5);
+      assertFalse(explanation.isMatch());
+      assertEquals(explanation.getDescription(), "Not a match");
+    }
+
+    w.close();
+    indexSearcher.getIndexReader().close();
+    dir.close();
+  }
+
   public void testRandomOrdinalsJoin() throws Exception {
     IndexIterationContext context = createContext(512, false, true);
     int searchIters = 10;