From f5d4397e5c4f6b644e0dbae453605fc68e46327d Mon Sep 17 00:00:00 2001
From: Awni Hannun <awni@apple.com>
Date: Wed, 8 Oct 2025 11:23:46 -0700
Subject: [PATCH] Fix fast synch when fence is waited before a command buffer
 is created (#2657)

---
 mlx/backend/metal/device.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mlx/backend/metal/device.cpp b/mlx/backend/metal/device.cpp
index 352958a89..5f2bb73d3 100644
--- a/mlx/backend/metal/device.cpp
+++ b/mlx/backend/metal/device.cpp
@@ -471,6 +471,10 @@ void Device::end_encoding(int index) {
 CommandEncoder& Device::get_command_encoder(int index) {
   auto& stream = get_stream_(index);
   if (stream.encoder == nullptr) {
+    // Ensure there is an active command buffer
+    if (stream.buffer == nullptr) {
+      get_command_buffer(index);
+    }
     stream.encoder = std::make_unique<CommandEncoder>(stream);
     stream.fence = std::make_shared<Fence>(device_->newFence());
   }