diff --git a/packaging/windows/installer.nsh b/packaging/windows/installer.nsh
index 5dc1415..ddd97de 100644
--- a/packaging/windows/installer.nsh
+++ b/packaging/windows/installer.nsh
@@ -121,103 +121,72 @@ Var FinalInstDir
   ${EndIf}
 !macroend
 
-; Returns 0 in $R9 when $R8 can be renamed (file unlocked / path free).
-; _ID must be unique per insert so labels do not collide.
-!macro tryRenameProbe _ID
-  StrCpy $R9 1
-  ${IfNot} ${FileExists} "$R8"
-    StrCpy $R9 0
-    Goto try_rename_probe_done_${_ID}
-  ${EndIf}
-
-  ClearErrors
-  Rename "$R8" "$R8.updating"
-  ${If} ${Errors}
-    Goto try_rename_probe_done_${_ID}
-  ${EndIf}
-
-  ; Leave the .updating name — the whole tree is about to be deleted.
-  StrCpy $R9 0
-  try_rename_probe_done_${_ID}:
-!macroend
-
-; Wait until the live install directory is released by the quitting app.
-!macro waitForInstallDirWritable
-  !insertmacro progressStatus "Waiting for Farm Control to release install files..."
-  DetailPrint "Waiting for install directory to become writable..."
-
-  StrCpy $R7 0
-  wait_install_writable:
-    ; Probe the main binaries — rename fails while the process still holds them.
-    StrCpy $R8 "$FinalInstDir\bin\FarmControl.exe"
-    !insertmacro tryRenameProbe farmcontrol
-    ${If} $R9 != 0
-      Goto wait_install_writable_retry
-    ${EndIf}
-
-    StrCpy $R8 "$FinalInstDir\bin\launcher.exe"
-    !insertmacro tryRenameProbe launcher
-    ${If} $R9 != 0
-      Goto wait_install_writable_retry
-    ${EndIf}
-
-    ; Also probe creating a temp file in the install root.
-    ClearErrors
-    FileOpen $R8 "$FinalInstDir\.farmcontrol-write-probe" w
-    ${If} $R8 == ""
-      Goto wait_install_writable_retry
-    ${EndIf}
-    FileClose $R8
-    Delete "$FinalInstDir\.farmcontrol-write-probe"
-    Goto wait_install_writable_done
-
-    wait_install_writable_retry:
-      IntOp $R7 $R7 + 1
-      ${If} $R7 < 60
-        Sleep 500
-        Goto wait_install_writable
-      ${EndIf}
-      !insertmacro progressFailure "Could not access the previous Farm Control installation."
-      Abort
-
-  wait_install_writable_done:
-!macroend
-
+; Swap order: Farm Control -> .old, Farm Control.new -> Farm Control, delete .old.
 !macro swapUpdateStaging
   !insertmacro progressPhase "Applying update"
+  !insertmacro progressStatus "Replacing Farm Control with the new version..."
+  DetailPrint "Replacing Farm Control with staged update..."
+
+  ; Clear a leftover .old from a previous interrupted update.
+  ${If} ${FileExists} "$FinalInstDir.old"
+    DetailPrint "Removing leftover Farm Control.old..."
+    RMDir /r "$FinalInstDir.old"
+  ${EndIf}
 
   ${If} ${FileExists} "$FinalInstDir"
-    !insertmacro waitForInstallDirWritable
-
-    !insertmacro progressStatus "Replacing Farm Control with the new version..."
-    DetailPrint "Replacing Farm Control with staged update..."
+    !insertmacro progressStatus "Waiting for Farm Control to release install files..."
+    DetailPrint "Waiting to rename install directory to Farm Control.old..."
 
     StrCpy $R7 0
-    swap_delete_retry:
-      RMDir /r "$FinalInstDir"
-      ${If} ${FileExists} "$FinalInstDir"
+    swap_rename_old_retry:
+      ClearErrors
+      Rename "$FinalInstDir" "$FinalInstDir.old"
+      ${If} ${Errors}
         IntOp $R7 $R7 + 1
-        ${If} $R7 < 20
+        ${If} $R7 < 60
           Sleep 500
-          Goto swap_delete_retry
+          Goto swap_rename_old_retry
         ${EndIf}
-        !insertmacro progressFailure "Could not remove the previous Farm Control installation."
+        !insertmacro progressFailure "Could not move the previous Farm Control installation aside."
         Abort
       ${EndIf}
   ${EndIf}
 
   !insertmacro progressStatus "Activating new Farm Control installation..."
-  DetailPrint "Activating staged update..."
+  DetailPrint "Renaming Farm Control.new to Farm Control..."
 
   ClearErrors
   Rename "$INSTDIR" "$FinalInstDir"
   ${If} ${Errors}
+    ; Best-effort rollback so the previous install is usable again.
+    ${If} ${FileExists} "$FinalInstDir.old"
+      Rename "$FinalInstDir.old" "$FinalInstDir"
+    ${EndIf}
     !insertmacro progressFailure "Could not activate the new Farm Control installation."
     Abort
   ${EndIf}
 
   StrCpy $INSTDIR $FinalInstDir
   !insertmacro progressLog "installer:STATUS:Update files activated"
+
+  ${If} ${FileExists} "$FinalInstDir.old"
+    !insertmacro progressStatus "Removing previous Farm Control installation..."
+    DetailPrint "Removing Farm Control.old..."
+
+    StrCpy $R7 0
+    swap_delete_old_retry:
+      RMDir /r "$FinalInstDir.old"
+      ${If} ${FileExists} "$FinalInstDir.old"
+        IntOp $R7 $R7 + 1
+        ${If} $R7 < 20
+          Sleep 500
+          Goto swap_delete_old_retry
+        ${EndIf}
+        ; New version is already active; leftover .old is non-fatal.
+        DetailPrint "Warning: could not fully remove Farm Control.old"
+        !insertmacro progressLog "installer:STATUS:Warning: could not fully remove previous installation"
+      ${EndIf}
+  ${EndIf}
 !macroend
 
 !macro uninstallPreviousFarmControl