diff --git a/google-cloud-firestore/clirr-ignored-differences.xml b/google-cloud-firestore/clirr-ignored-differences.xml
index 7a4c83689..3c42178c0 100644
--- a/google-cloud-firestore/clirr-ignored-differences.xml
+++ b/google-cloud-firestore/clirr-ignored-differences.xml
@@ -299,4 +299,11 @@
     <className>com/google/cloud/firestore/collection/StandardComparator</className>
     <to>*</to>
   </difference>
+
+  <!-- Reverted a change to make CustomClassMapper public -->
+  <difference>
+    <differenceType>8001</differenceType>
+    <className>com/google/cloud/firestore/encoding/CustomClassMapper</className>
+    <to>*</to>
+  </difference>
 </differences>