diff --git a/crates/ml-dqn/src/gpu_replay_buffer.rs b/crates/ml-dqn/src/gpu_replay_buffer.rs
index 852e7ce8c..607caf604 100644
--- a/crates/ml-dqn/src/gpu_replay_buffer.rs
+++ b/crates/ml-dqn/src/gpu_replay_buffer.rs
@@ -753,9 +753,11 @@ impl GpuReplayBuffer {
         let stream_owned = ext_stream.cloned().unwrap_or_else(|| Arc::clone(&self.stream));
         let stream = &stream_owned;
         // Convert bf16 td_errors to f32 using pre-allocated scratch buffer
-        eprintln!("PER_DIAG: getting cast kernels");
-        let kernels = get_cast_kernels(stream)?;
-        eprintln!("PER_DIAG: launching bf16_to_f32 cast");
+        eprintln!("PER_DIAG: getting cast kernels (using self.stream for module load)");
+        // Use self.stream for kernel compilation (needs bound context).
+        // ext_stream is only used for kernel launches.
+        let kernels = get_cast_kernels(&self.stream)?;
+        eprintln!("PER_DIAG: launching bf16_to_f32 cast on ext_stream");
         let ni = bs as i32;
         // SAFETY: update_td_f32, td_errors are valid device allocations of at least bs elements.
         unsafe {