diff --git a/cdm/core/src/main/java/thredds/filesystem/MFileOS.java b/cdm/core/src/main/java/thredds/filesystem/MFileOS.java
index 3bb3e7ff1a..094a02f6ec 100644
--- a/cdm/core/src/main/java/thredds/filesystem/MFileOS.java
+++ b/cdm/core/src/main/java/thredds/filesystem/MFileOS.java
@@ -88,9 +88,11 @@ public String getName() {
     return file.getName();
   }
 
+  @Nullable
   @Override
   public MFile getParent() {
-    return new MFileOS(file.getParentFile());
+    File parent = file.getParentFile();
+    return parent == null ? null : new MFileOS(parent);
   }
 
   @Override