diff --git a/litellm/proxy/proxy_server.py b/litellm/proxy/proxy_server.py
index c96d0acb008..2d25f98f8a4 100644
--- a/litellm/proxy/proxy_server.py
+++ b/litellm/proxy/proxy_server.py
@@ -6524,6 +6524,18 @@ async def async_data_generator(
 
             if isinstance(chunk, BaseModel):
                 chunk = chunk.model_dump_json(exclude_none=True, exclude_unset=True)
+            elif isinstance(chunk, bytes):
+                # Some upstream streaming iterators (e.g. AsyncGoogleGenAIGenerateContentStreamingIterator
+                # for /v1beta/.../streamGenerateContent) yield raw SSE bytes from Gemini.
+                # Decode to str so the f-string below does not emit a Python b'...' literal,
+                # and pass already-formatted SSE through unchanged to avoid double "data:" prefix.
+                chunk = chunk.decode("utf-8", errors="replace")
+                if chunk.startswith(("data:", "event:", ":")):
+                    try:
+                        yield chunk if chunk.endswith("\n\n") else chunk + "\n\n"
+                    except Exception as e:
+                        yield f"data: {str(e)}\n\n"
+                    continue
             elif isinstance(chunk, str) and chunk.startswith("data: "):
                 error_message = chunk
                 break