diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 79c7266bb37..c6f646eba24 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -131,6 +131,8 @@ Bug Fixes
 
 * LUCENE-10607: Fix potential integer overflow in maxArcs computions (Tang Donghai)
 
+* GITHUB#986: Fix FieldExistsQuery rewrite when all docs have vectors. (Julie Tibshirani)
+
 Other
 ---------------------
 
diff --git a/lucene/core/src/java/org/apache/lucene/search/FieldExistsQuery.java b/lucene/core/src/java/org/apache/lucene/search/FieldExistsQuery.java
index f5c2b08c5f6..5a3d8b755b3 100644
--- a/lucene/core/src/java/org/apache/lucene/search/FieldExistsQuery.java
+++ b/lucene/core/src/java/org/apache/lucene/search/FieldExistsQuery.java
@@ -126,7 +126,7 @@ public class FieldExistsQuery extends Query {
           break;
         }
       } else if (fieldInfo.getVectorDimension() != 0) { // the field indexes vectors
-        if (leaf.getVectorValues(field).size() != reader.maxDoc()) {
+        if (leaf.getVectorValues(field).size() != leaf.maxDoc()) {
           allReadersRewritable = false;
           break;
         }
diff --git a/lucene/core/src/test/org/apache/lucene/search/TestFieldExistsQuery.java b/lucene/core/src/test/org/apache/lucene/search/TestFieldExistsQuery.java
index cbbccf35595..0cb43864948 100644
--- a/lucene/core/src/test/org/apache/lucene/search/TestFieldExistsQuery.java
+++ b/lucene/core/src/test/org/apache/lucene/search/TestFieldExistsQuery.java
@@ -626,13 +626,18 @@ public class TestFieldExistsQuery extends LuceneTestCase {
   public void testKnnVectorAllDocsHaveField() throws IOException {
     try (Directory dir = newDirectory();
         RandomIndexWriter iw = new RandomIndexWriter(random(), dir)) {
-      Document doc = new Document();
-      doc.add(new KnnVectorField("vector", randomVector(3)));
-      iw.addDocument(doc);
+      for (int i = 0; i < 100; ++i) {
+        Document doc = new Document();
+        doc.add(new KnnVectorField("vector", randomVector(5)));
+        iw.addDocument(doc);
+      }
       iw.commit();
+
       try (IndexReader reader = iw.getReader()) {
         IndexSearcher searcher = newSearcher(reader);
-        assertEquals(1, searcher.count(new FieldExistsQuery("vector")));
+        Query query = new FieldExistsQuery("vector");
+        assertTrue(searcher.rewrite(query) instanceof MatchAllDocsQuery);
+        assertEquals(100, searcher.count(query));
       }
     }
   }