diff --git a/projects/blenderbot2/agents/modules.py b/projects/blenderbot2/agents/modules.py
index cc8924f43f9..accc5390a81 100644
--- a/projects/blenderbot2/agents/modules.py
+++ b/projects/blenderbot2/agents/modules.py
@@ -828,6 +828,8 @@ def __init__(self, opt: Opt, null_idx: int):
 class BlenderBot2FidModelMixin:
     embedding_size: int
     pad_idx: int
+    long_term_memory: LongTermMemory
+    retriever: RagRetriever
 
     def __init__(self, opt: Opt, dictionary: DictionaryAgent, retriever_shared=None):
         super().__init__(
@@ -837,6 +839,12 @@ def __init__(self, opt: Opt, dictionary: DictionaryAgent, retriever_shared=None)
             opt, dictionary[dictionary.null_token]
         )
         self.embedding_size = opt['embedding_size']
+        for param in self.long_term_memory.query_encoder.parameters():
+            param.requires_grad = False
+        for param in self.long_term_memory.memory_encoder.parameters():
+            param.requires_grad = False
+        for param in self.retriever.parameters():
+            param.requires_grad = False
 
     def encoder(
         self,
@@ -935,4 +943,12 @@ class BB2SearchQueryFaissIndexRetriever(
 class BB2ObservationEchoRetriever(BB2SearchRetrieverMixin, ObservationEchoRetriever):
     """
     A retriever that reads retrieved docs as part of the observed example message.
+
+    Provides backwards compatibility with BB2 models by instantiating a query encoder.
     """
+
+    def __init__(self, opt: Opt, dictionary: DictionaryAgent, shared=None):
+        super().__init__(opt, dictionary, shared)
+        self.query_encoder = DprQueryEncoder(
+            opt, dpr_model=opt['query_model'], pretrained_path=opt['dpr_model_file']
+        )