diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 8a094e695c9..c2a3cca1c82 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -168,6 +168,9 @@ Bug Fixes:
  * LUCENE-8381: Fix IndexWriter incorrectly interprets hard-deletes as soft-deletes
    while wrapping reader for merges. (Simon Willnauer, Nhat Nguyen)
 
+ * LUCENE-8384: Fix missing advance docValues generation while handling docValues
+   update in PendingSoftDeletes. (Simon Willnauer, Nhat Nguyen)
+
 ======================= Lucene 7.4.0 =======================
 
 Upgrading
diff --git a/lucene/core/src/java/org/apache/lucene/index/PendingSoftDeletes.java b/lucene/core/src/java/org/apache/lucene/index/PendingSoftDeletes.java
index 4074903a363..eb6e4ff3604 100644
--- a/lucene/core/src/java/org/apache/lucene/index/PendingSoftDeletes.java
+++ b/lucene/core/src/java/org/apache/lucene/index/PendingSoftDeletes.java
@@ -146,12 +146,12 @@ final class PendingSoftDeletes extends PendingDeletes {
     if (this.field.equals(info.name)) {
       pendingDeleteCount += applySoftDeletes(iterator, getMutableBits());
       assert assertPendingDeletes();
-      assert dvGeneration < info.getDocValuesGen() : "we have seen this generation update already: " + dvGeneration + " vs. " + info.getDocValuesGen();
-      assert dvGeneration != -2 : "docValues generation is still uninitialized";
-      dvGeneration = info.getDocValuesGen();
       this.info.setSoftDelCount(this.info.getSoftDelCount() + pendingDeleteCount);
       super.dropChanges();
     }
+    assert dvGeneration < info.getDocValuesGen() : "we have seen this generation update already: " + dvGeneration + " vs. " + info.getDocValuesGen();
+    assert dvGeneration != -2 : "docValues generation is still uninitialized";
+    dvGeneration = info.getDocValuesGen();
   }
 
   private boolean assertPendingDeletes() {
diff --git a/lucene/core/src/java/org/apache/lucene/index/SegmentCommitInfo.java b/lucene/core/src/java/org/apache/lucene/index/SegmentCommitInfo.java
index 954a1382a48..69117574698 100644
--- a/lucene/core/src/java/org/apache/lucene/index/SegmentCommitInfo.java
+++ b/lucene/core/src/java/org/apache/lucene/index/SegmentCommitInfo.java
@@ -328,7 +328,7 @@ public class SegmentCommitInfo {
     if (delCount < 0 || delCount > info.maxDoc()) {
       throw new IllegalArgumentException("invalid delCount=" + delCount + " (maxDoc=" + info.maxDoc() + ")");
     }
-    assert softDelCount + delCount <= info.maxDoc();
+    assert softDelCount + delCount <= info.maxDoc() : "maxDoc=" + info.maxDoc() + ",delCount=" + delCount + ",softDelCount=" + softDelCount;
     this.delCount = delCount;
   }
 
@@ -336,7 +336,7 @@ public class SegmentCommitInfo {
     if (softDelCount < 0 || softDelCount > info.maxDoc()) {
       throw new IllegalArgumentException("invalid softDelCount=" + softDelCount + " (maxDoc=" + info.maxDoc() + ")");
     }
-    assert softDelCount + delCount <= info.maxDoc();
+    assert softDelCount + delCount <= info.maxDoc() : "maxDoc=" + info.maxDoc() + ",delCount=" + delCount + ",softDelCount=" + softDelCount;
     this.softDelCount = softDelCount;
   }
 
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestSoftDeletesRetentionMergePolicy.java b/lucene/core/src/test/org/apache/lucene/index/TestSoftDeletesRetentionMergePolicy.java
index bb36ba300f0..ee2b6508585 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestSoftDeletesRetentionMergePolicy.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestSoftDeletesRetentionMergePolicy.java
@@ -40,6 +40,8 @@ import org.apache.lucene.search.IndexSearcher;
 import org.apache.lucene.search.MatchAllDocsQuery;
 import org.apache.lucene.search.MatchNoDocsQuery;
 import org.apache.lucene.search.Query;
+import org.apache.lucene.search.SearcherFactory;
+import org.apache.lucene.search.SearcherManager;
 import org.apache.lucene.search.TermQuery;
 import org.apache.lucene.search.TopDocs;
 import org.apache.lucene.store.Directory;
@@ -607,6 +609,26 @@ public class TestSoftDeletesRetentionMergePolicy extends LuceneTestCase {
     IOUtils.close(writer, dir);
   }
 
+  public void testSoftDeleteWithTryUpdateDocValue() throws Exception {
+    Directory dir = newDirectory();
+    IndexWriterConfig config = newIndexWriterConfig().setSoftDeletesField("soft_delete")
+        .setMergePolicy(new SoftDeletesRetentionMergePolicy("soft_delete", MatchAllDocsQuery::new, newLogMergePolicy()));
+    IndexWriter writer = new IndexWriter(dir, config);
+    SearcherManager sm = new SearcherManager(writer, new SearcherFactory());
+    Document d = new Document();
+    d.add(new StringField("id", "0", Field.Store.YES));
+    writer.addDocument(d);
+    sm.maybeRefreshBlocking();
+    doUpdate(new Term("id", "0"), writer,
+        new NumericDocValuesField("soft_delete", 1), new NumericDocValuesField("other-field", 1));
+    sm.maybeRefreshBlocking();
+    assertEquals(1, writer.segmentInfos.asList().size());
+    SegmentCommitInfo si = writer.segmentInfos.asList().get(0);
+    assertEquals(1, si.getSoftDelCount());
+    assertEquals(1, si.info.maxDoc());
+    IOUtils.close(sm, writer, dir);
+  }
+
   static void doUpdate(Term doc, IndexWriter writer, Field... fields) throws IOException {
     long seqId = -1;
     do { // retry if we just committing a merge