diff --git a/drivers/storage/ahcid/src/main.rs b/drivers/storage/ahcid/src/main.rs
index 1f130a2974..e3b82d612d 100644
--- a/drivers/storage/ahcid/src/main.rs
+++ b/drivers/storage/ahcid/src/main.rs
@@ -91,11 +91,22 @@ fn daemon(daemon: daemon::Daemon, mut pcid_handle: PciFunctionHandle) -> ! {
                             }
                         }
                         hba_mem.is.write(is);
+                    }
 
-                        irq_file
-                            .write(&irq)
-                            .expect("ahcid: failed to write irq file");
+                    // The kernel masks the IRQ line when it delivers the interrupt to us and
+                    // only re-enables it once we write the count back (that write maps to
+                    // acknowledge() -> pic_unmask()/ioapic_unmask()). IRQ lines are shared, so
+                    // an interrupt raised by a *different* device arrives here with is == 0.
+                    // Acking only inside the `is > 0` branch meant one foreign interrupt left
+                    // the line masked forever: every later AHCI completion was lost and all
+                    // disk I/O blocked permanently. Always re-arm the line, whether or not the
+                    // interrupt turned out to be ours. Device-level status is cleared above
+                    // before we unmask, so this cannot re-trigger a storm.
+                    irq_file
+                        .write(&irq)
+                        .expect("ahcid: failed to write irq file");
 
+                    if is > 0 {
                         FuturesExecutor.block_on(scheme.tick()).unwrap();
                     }
                 }