diff --git a/server/src/main/java/org/elasticsearch/index/mapper/PassThroughObjectMapper.java b/server/src/main/java/org/elasticsearch/index/mapper/PassThroughObjectMapper.java
index 2a2bad360e264..d44f03d72e211 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/PassThroughObjectMapper.java
+++ b/server/src/main/java/org/elasticsearch/index/mapper/PassThroughObjectMapper.java
@@ -99,9 +99,14 @@ public PassThroughObjectMapper.Builder newBuilder(IndexVersion indexVersionCreat
         return builder;
     }
 
-    public PassThroughObjectMapper merge(ObjectMapper mergeWith, MapperMergeContext parentBuilderContext) {
-        final var mergeResult = MergeResult.build(this, mergeWith, parentBuilderContext);
+    @Override
+    public PassThroughObjectMapper merge(Mapper mergeWith, MapperMergeContext parentBuilderContext) {
+        if (mergeWith instanceof PassThroughObjectMapper == false) {
+            MapperErrors.throwObjectMappingConflictError(mergeWith.name());
+        }
+
         PassThroughObjectMapper mergeWithObject = (PassThroughObjectMapper) mergeWith;
+        final var mergeResult = MergeResult.build(this, mergeWithObject, parentBuilderContext);
 
         final Explicit<Boolean> containsDimensions = (mergeWithObject.timeSeriesDimensionSubFields.explicit())
             ? mergeWithObject.timeSeriesDimensionSubFields
diff --git a/server/src/main/java/org/elasticsearch/index/mapper/RootObjectMapper.java b/server/src/main/java/org/elasticsearch/index/mapper/RootObjectMapper.java
index b91e32a158fe6..8db3a970e31c8 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/RootObjectMapper.java
+++ b/server/src/main/java/org/elasticsearch/index/mapper/RootObjectMapper.java
@@ -344,6 +344,7 @@ protected MapperMergeContext createChildContext(MapperMergeContext mapperMergeCo
         return mapperMergeContext.createChildContext(null, dynamic);
     }
 
+    @Override
     public RootObjectMapper merge(Mapper mergeWith, MapperMergeContext parentMergeContext) {
         if (mergeWith instanceof RootObjectMapper == false) {
             MapperErrors.throwObjectMappingConflictError(mergeWith.name());