diff --git a/lucene/core/src/java/org/apache/lucene/store/FileSwitchDirectory.java b/lucene/core/src/java/org/apache/lucene/store/FileSwitchDirectory.java
index eb3fa0f6f24..db9f08542d9 100644
--- a/lucene/core/src/java/org/apache/lucene/store/FileSwitchDirectory.java
+++ b/lucene/core/src/java/org/apache/lucene/store/FileSwitchDirectory.java
@@ -21,6 +21,7 @@ import java.io.IOException;
 import java.nio.file.AtomicMoveNotSupportedException;
 import java.nio.file.NoSuchFileException;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collection;
 import java.util.HashSet;
 import java.util.List;
@@ -118,7 +119,9 @@ public class FileSwitchDirectory extends Directory {
     if (exc != null && files.isEmpty()) {
       throw exc;
     }
-    return files.toArray(new String[files.size()]);
+    String[] result = files.toArray(new String[files.size()]);
+    Arrays.sort(result);
+    return result;
   }
 
   /** Utility method to return a file's extension. */
diff --git a/lucene/core/src/java/org/apache/lucene/store/NRTCachingDirectory.java b/lucene/core/src/java/org/apache/lucene/store/NRTCachingDirectory.java
index 4f3b25422cc..ef7b895af76 100644
--- a/lucene/core/src/java/org/apache/lucene/store/NRTCachingDirectory.java
+++ b/lucene/core/src/java/org/apache/lucene/store/NRTCachingDirectory.java
@@ -106,7 +106,9 @@ public class NRTCachingDirectory extends FilterDirectory implements Accountable
                                         "cache=" + Arrays.toString(cache.listAll()) + ",delegate=" + Arrays.toString(in.listAll()));
       }
     }
-    return files.toArray(new String[files.size()]);
+    String[] result = files.toArray(new String[files.size()]);
+    Arrays.sort(result);
+    return result;
   }
 
   @Override
diff --git a/lucene/test-framework/src/java/org/apache/lucene/store/BaseDirectoryTestCase.java b/lucene/test-framework/src/java/org/apache/lucene/store/BaseDirectoryTestCase.java
index c2e199698dd..3d9c20dd46f 100644
--- a/lucene/test-framework/src/java/org/apache/lucene/store/BaseDirectoryTestCase.java
+++ b/lucene/test-framework/src/java/org/apache/lucene/store/BaseDirectoryTestCase.java
@@ -1295,4 +1295,30 @@ public abstract class BaseDirectoryTestCase extends LuceneTestCase {
       assertTrue(Arrays.asList(fsDir.listAll()).contains(fileName));
     }
   }
+
+  public void testListAllIsSorted() throws IOException {
+    try (Directory dir = getDirectory(createTempDir())) {
+      int count = atLeast(20);
+      Set<String> names = new HashSet<>();
+      while(names.size() < count) {
+        String name = TestUtil.randomSimpleString(random());
+        if (name.length() == 0) {
+          continue;
+        }
+        if (random().nextInt(5) == 1) {
+          IndexOutput out = dir.createTempOutput(name, "foo", IOContext.DEFAULT);
+          names.add(out.getName());
+          out.close();
+        } else if (names.contains(name) == false) {
+          IndexOutput out = dir.createOutput(name, IOContext.DEFAULT);
+          names.add(out.getName());
+          out.close();
+        }
+      }
+      String[] actual = dir.listAll();
+      String[] expected = actual.clone();
+      Arrays.sort(expected);
+      assertEquals(expected, actual);
+    }
+  }
 }