diff --git a/apps/machine/electron/hal-service.ts b/apps/machine/electron/hal-service.ts
index 2ec863b..1259c77 100644
--- a/apps/machine/electron/hal-service.ts
+++ b/apps/machine/electron/hal-service.ts
@@ -376,12 +376,10 @@ export async function initializeHal(config: HalConfig): Promise<HalInstance> {
     setCassettes: async (cassettes: CassetteConfig[]): Promise<void> => {
       console.log(
         '[HAL] Hot-reloading cassette layout:',
-        cassettes
-          .map((c) => `bay${c.position}:${c.denomination}×${c.count ?? 0}`)
-          .join(', ')
+        cassettes.map((c) => `bay${c.position}:${c.denomination}×${c.count ?? 0}`).join(', ')
       )
-      // Rebuild bays first so subsequent dispense calls see the new layout
-      // even if the dispenser re-init is slow / fails.
+      const previousBays = bays
+      const previousInitData = dispenserInitData
       bays = cassettes
         .slice()
         .sort((a, b) => a.position - b.position)
@@ -391,31 +389,40 @@ export async function initializeHal(config: HalConfig): Promise<HalInstance> {
           count: c.count ?? 0,
         }))
       dispenserInitData = { fiatCode: valConfig.fiatCode, cassettes }
-      // Close + re-init the dispenser so its internal per-bay state matches
-      // the new layout. Errors here surface to the caller (operator-config
-      // consumer) — the renderer can decide whether to retry.
+      // Close + re-init the dispenser so its internal per-bay state matches the
+      // new layout. close() now resolves only once the port is really closed,
+      // so the re-open below cannot race it (aiolabs/bitspire#118).
+      //
+      // On failure, roll the in-memory layout back. This reverses an earlier
+      // deliberate choice to keep the new bays "even if the dispenser re-init
+      // is slow / fails": with the re-init failing every time on douro, the app
+      // kept a layout the device had never taken and the operator-config
+      // consumer went on to publish a cassettes-state event advertising it. A
+      // subsequent dispense would then pick bays by a layout the hardware does
+      // not share. Better to surface the failure and stay truthful about what
+      // the device is actually running.
       try {
-        dispenser.close()
+        await dispenser.close()
+        await dispenser.init(dispenserInitData)
       } catch (err) {
-        console.warn('[HAL] Dispenser close during setCassettes raised:', err)
+        bays = previousBays
+        dispenserInitData = previousInitData
+        console.error('[HAL] Dispenser re-init failed; keeping the previous cassette layout:', err)
+        throw err
       }
-      await dispenser.init(dispenserInitData)
       console.log('[HAL] Dispenser re-initialized with new cassettes')
     },
 
     cleanup: async () => {
-      return new Promise<void>((resolve) => {
-        validator?.disable()
-        validator?.lightOff()
-        dispenser.close()
-        if (validator) {
-          validator.close((err?: Error) => {
-            if (err) console.error('[HAL] Validator close error:', err)
-            resolve()
-          })
-        } else {
+      validator?.disable()
+      validator?.lightOff()
+      await dispenser.close()
+      if (!validator) return
+      await new Promise<void>((resolve) => {
+        validator?.close((err?: Error) => {
+          if (err) console.error('[HAL] Validator close error:', err)
           resolve()
-        }
+        })
       })
     },
   }