diff --git a/master_changes.md b/master_changes.md
index 27fe6319526..55d9f2c9957 100644
--- a/master_changes.md
+++ b/master_changes.md
@@ -87,6 +87,7 @@ users)
   * Pass --symlink-type native to Cygwin setup if symlinks are available [#5830 @dra27]
   * Pass --no-version-check to Cygwin setup (suppresses a message box if setup needs updating) [#5830 @dra27]
   * Pass --quiet-mode noinput to stop the user interrupting the setup GUI [#5830 @dra27]
+  * Always pass --no-write-registry to the Cygwin installer, not just on first installation [#5995 @dra27]
 
 ## Format upgrade
   * Handle init OCaml `sys-ocaml-*` eval variables during format upgrade from 2.0 -> 2.1 -> 2.2 [#5829 @dra27]
diff --git a/src/state/opamSysInteract.ml b/src/state/opamSysInteract.ml
index 9d48d0f62d3..0a780db827f 100644
--- a/src/state/opamSysInteract.ml
+++ b/src/state/opamSysInteract.ml
@@ -984,6 +984,7 @@ let install_packages_commands_t ?(env=OpamVariable.Map.empty) config sys_package
             let common =
               [ "--upgrade-also";
                 "--only-site";
+                "--no-write-registry";
                 "--no-version-check";
                 "--site"; Cygwin.mirror;
                 "--local-package-dir";