diff --git a/agentplatform/preview/rag/utils/_gapic_utils.py b/agentplatform/preview/rag/utils/_gapic_utils.py
index ef3d166730..d3e5611c46 100644
--- a/agentplatform/preview/rag/utils/_gapic_utils.py
+++ b/agentplatform/preview/rag/utils/_gapic_utils.py
@@ -1298,7 +1298,7 @@ def set_backend_config(
     if backend_config.vector_db is not None:
         vector_config = backend_config.vector_db
         if vector_config is None:
-            rag_corpus.vector_db_config.rag_managed_db.CopyFrom(
+            rag_corpus.vector_db_config.rag_managed_db = (
                 GapicRagVectorDbConfig.RagManagedDb()
             )
         elif isinstance(vector_config, RagManagedDb):
diff --git a/agentplatform/rag/utils/_gapic_utils.py b/agentplatform/rag/utils/_gapic_utils.py
index 1077f47592..0a6476b943 100644
--- a/agentplatform/rag/utils/_gapic_utils.py
+++ b/agentplatform/rag/utils/_gapic_utils.py
@@ -700,7 +700,7 @@ def set_backend_config(
     if backend_config.vector_db is not None:
         vector_config = backend_config.vector_db
         if isinstance(vector_config, RagManagedDb):
-            rag_corpus.vector_db_config.rag_managed_db.CopyFrom(
+            rag_corpus.vector_db_config.rag_managed_db = (
                 GapicRagVectorDbConfig.RagManagedDb()
             )
         elif isinstance(vector_config, VertexVectorSearch):
diff --git a/tests/unit/vertex_rag/test_rag_data.py b/tests/unit/vertex_rag/test_rag_data.py
index 763d03a92d..41d406f922 100644
--- a/tests/unit/vertex_rag/test_rag_data.py
+++ b/tests/unit/vertex_rag/test_rag_data.py
@@ -490,6 +490,18 @@ def test_create_corpus_success(self):
 
         rag_corpus_eq(rag_corpus, test_rag_constants.TEST_RAG_CORPUS)
 
+    @pytest.mark.usefixtures("create_rag_corpus_mock")
+    def test_create_corpus_rag_managed_db_success(self):
+        backend_config = rag.RagVectorDbConfig(
+            vector_db=rag.RagManagedDb()
+        )
+        rag_corpus = rag.create_corpus(
+            display_name=test_rag_constants.TEST_CORPUS_DISPLAY_NAME,
+            backend_config=backend_config,
+        )
+
+        rag_corpus_eq(rag_corpus, test_rag_constants.TEST_RAG_CORPUS)
+
     @pytest.mark.usefixtures("create_rag_corpus_mock_vertex_vector_search")
     def test_create_corpus_vertex_vector_search_success(self):
         rag_corpus = rag.create_corpus(
diff --git a/vertexai/preview/rag/utils/_gapic_utils.py b/vertexai/preview/rag/utils/_gapic_utils.py
index 273b415432..ea9f003712 100644
--- a/vertexai/preview/rag/utils/_gapic_utils.py
+++ b/vertexai/preview/rag/utils/_gapic_utils.py
@@ -1304,7 +1304,7 @@ def set_backend_config(
     if backend_config.vector_db is not None:
         vector_config = backend_config.vector_db
         if vector_config is None:
-            rag_corpus.vector_db_config.rag_managed_db.CopyFrom(
+            rag_corpus.vector_db_config.rag_managed_db = (
                 GapicRagVectorDbConfig.RagManagedDb()
             )
         elif isinstance(vector_config, RagManagedDb):
diff --git a/vertexai/rag/utils/_gapic_utils.py b/vertexai/rag/utils/_gapic_utils.py
index ea140a7c88..83b63cc376 100644
--- a/vertexai/rag/utils/_gapic_utils.py
+++ b/vertexai/rag/utils/_gapic_utils.py
@@ -702,7 +702,7 @@ def set_backend_config(
     if backend_config.vector_db is not None:
         vector_config = backend_config.vector_db
         if isinstance(vector_config, RagManagedDb):
-            rag_corpus.vector_db_config.rag_managed_db.CopyFrom(
+            rag_corpus.vector_db_config.rag_managed_db = (
                 GapicRagVectorDbConfig.RagManagedDb()
             )
         elif isinstance(vector_config, VertexVectorSearch):