diff --git a/core/dr-gpu/src/adjust.rs b/core/dr-gpu/src/adjust.rs
index 245100c..7d7cda0 100644
--- a/core/dr-gpu/src/adjust.rs
+++ b/core/dr-gpu/src/adjust.rs
@@ -31,6 +31,15 @@ use crate::{DemosaicedImage, GpuContext, GpuError};
 /// reads them.
 const RESERVED_FIELDS: usize = dr_pipeline::RESERVED_UNIFORM_FIELDS;
 
+/// How many non-blocking polls a readback gets before it is called failed.
+///
+/// A bound rather than a spin forever: if the device is lost the map callback
+/// never arrives, and an unbounded loop would hang the interface rather than
+/// surfacing the error. Set far above any plausible completion — the copy this
+/// waits on is milliseconds — so it is reached only when something is wrong.
+#[cfg(any(test, feature = "readback"))]
+const READBACK_POLL_LIMIT: u32 = 100_000;
+
 /// Runs composed operation chains against demosaiced images.
 pub struct AdjustPass {
     ctx: GpuContext,
@@ -353,9 +362,32 @@ impl AdjustPass {
         slice.map_async(wgpu::MapMode::Read, move |r| {
             let _ = tx.send(r);
         });
-        self.ctx.device.poll(wgpu::Maintain::Wait);
-        rx.recv()
-            .map_err(|e| GpuError::Readback(e.to_string()))?
+
+        // **Polled without blocking, then checked.**
+        //
+        // `Maintain::Wait` parks the calling thread until the GPU has finished,
+        // and this is called from the UI thread — so that park was a frozen
+        // interface for the duration of the copy (~7 ms at 4K, per the note
+        // above). `Poll` drives the same callbacks without sleeping, so the
+        // loop below stays interruptible and the mapping still completes.
+        //
+        // The bounded spin matters: a lost device would otherwise never
+        // deliver the callback and this would hang the app instead of
+        // reporting an error.
+        let mut mapped = None;
+        for _ in 0..READBACK_POLL_LIMIT {
+            self.ctx.device.poll(wgpu::Maintain::Poll);
+            match rx.try_recv() {
+                Ok(r) => {
+                    mapped = Some(r);
+                    break;
+                }
+                Err(std::sync::mpsc::TryRecvError::Empty) => continue,
+                Err(e) => return Err(GpuError::Readback(e.to_string())),
+            }
+        }
+        mapped
+            .ok_or_else(|| GpuError::Readback("readback did not complete".into()))?
             .map_err(|e| GpuError::Readback(e.to_string()))?;
 
         let data = slice.get_mapped_range();