diff --git a/cdm/core/src/test/java/thredds/filesystem/TestMFileOS.java b/cdm/core/src/test/java/thredds/filesystem/TestMFileOS.java
index d1a0af4d72..a12ae653fa 100644
--- a/cdm/core/src/test/java/thredds/filesystem/TestMFileOS.java
+++ b/cdm/core/src/test/java/thredds/filesystem/TestMFileOS.java
@@ -100,6 +100,14 @@ public void shouldGetChildMFile() {
       assertThat(newMFile.getParent().getPath()).isEqualTo(mFile.getPath());
       assertThat(newMFile.getPath()).isEqualTo(Paths.get(mFile.getPath(), "newFile").toString());
     }
+
+    @Test
+    public void shouldGetRelativePath() {
+      final MFileOS mFile = new MFileOS("/an/absolute/path/a/");
+      final MFileOS mFile2 = new MFileOS("/an/absolute/path/foo/bar/");
+      assertThat(mFile.relativize(mFile2)).isEqualTo("../foo/bar");
+      assertThat(mFile2.relativize(mFile)).isEqualTo("../../a");
+    }
   }
 
   private static File createTemporaryFile(int size) throws IOException {
diff --git a/cdm/core/src/test/java/thredds/filesystem/TestMFileOS7.java b/cdm/core/src/test/java/thredds/filesystem/TestMFileOS7.java
index f2ec53a261..6d001ffe03 100644
--- a/cdm/core/src/test/java/thredds/filesystem/TestMFileOS7.java
+++ b/cdm/core/src/test/java/thredds/filesystem/TestMFileOS7.java
@@ -98,6 +98,14 @@ public void shouldGetInputStream() throws IOException {
         assertThat(inputStream.read()).isNotEqualTo(-1);
       }
     }
+
+    @Test
+    public void shouldGetRelativePath() throws IOException {
+      final MFileOS7 mFile = new MFileOS7(Paths.get("/an/absolute/path"), null);
+      final MFileOS7 mFile2 = new MFileOS7(Paths.get("/an/absolute/path/foo"), null);
+      assertThat(mFile.relativize(mFile2)).isEqualTo("foo");
+      assertThat(mFile2.relativize(mFile)).isEqualTo("..");
+    }
   }
 
   private static File createTemporaryFile(int size) throws IOException {
diff --git a/cdm/s3/src/test/java/thredds/inventory/s3/TestMFileS3.java b/cdm/s3/src/test/java/thredds/inventory/s3/TestMFileS3.java
index e67ceed2b4..6334bdde53 100644
--- a/cdm/s3/src/test/java/thredds/inventory/s3/TestMFileS3.java
+++ b/cdm/s3/src/test/java/thredds/inventory/s3/TestMFileS3.java
@@ -516,7 +516,42 @@ private void checkS3MFilesAuxInfo(String uri) throws IOException {
   @RunWith(Parameterized.class)
   public static class TestMFileS3Parameterized {
 
+    @Parameterized.Parameters(name = "{0}, {1}, {2}")
+    public static List<Object[]> getTestParameters() {
+      return Arrays.asList(new Object[][] {
 
+          {"cdms3:bucket?a/long/key/", "cdms3:bucket?a/long/", ""},
+          {"cdms3:bucket?a/long/key/#delimiter=/", "cdms3:otherBucket?a/long/#delimiter=/", ""},
+          {"cdms3:bucket?a/long/#delimiter=/", "cdms3:bucket?a/long/key", ""},
+          {"cdms3:bucket", "cdms3:bucket?a/long/key", ""}, {"cdms3:bucket?a/long/key", "cdms3:bucket", ""},
+
+          {"cdms3:bucket?a/long/#delimiter=/", "cdms3:bucket?a/long/key/#delimiter=/", "key"},
+          {"cdms3:bucket?a/long/#delimiter=/", "cdms3:bucket?a/long/key#delimiter=/", "key"},
+          {"cdms3:bucket?a/long#delimiter=/", "cdms3:bucket?a/long/key/#delimiter=/", "key"},
+          {"cdms3:bucket?a/long#delimiter=/", "cdms3:bucket?a/long/key#delimiter=/", "key"},
+
+          {"cdms3:bucket?a/long/key/#delimiter=/", "cdms3:bucket?a/long/key/#delimiter=/", ""},
+          {"cdms3:bucket?a/long/key#delimiter=/", "cdms3:bucket?a/long#delimiter=/", ".."},
+          {"cdms3:bucket?a/long#delimiter=/", "cdms3:bucket?a/long_key#delimiter=/", "../long_key"},
+
+      });
+    }
+
+    @Parameterized.Parameter(value = 0)
+    public String uri1;
+
+    @Parameterized.Parameter(value = 1)
+    public String uri2;
+
+    @Parameterized.Parameter(value = 2)
+    public String expectedRelativePath;
+
+    @Test
+    public void shouldRelativizeKey() throws URISyntaxException, IOException {
+      final MFile mFile = new MFileS3(uri1);
+      final MFile mFile2 = new MFileS3(uri2);
+      assertThat(mFile.relativize(mFile2)).isEqualTo(expectedRelativePath);
+    }
   }
 
 }