diff --git a/rust/agama-dbus-server/src/locale.rs b/rust/agama-dbus-server/src/locale.rs
index cae074a708..aabdfdc260 100644
--- a/rust/agama-dbus-server/src/locale.rs
+++ b/rust/agama-dbus-server/src/locale.rs
@@ -156,19 +156,16 @@ impl Locale {
             .args([
                 "--root",
                 ROOT,
+                "--force",
                 "--locale",
                 self.locales.first().context("missing locale")?.as_str(),
+                "--keymap",
+                &self.keymap.to_string(),
+                "--timezone",
+                &self.timezone,
             ])
             .status()
             .context("Failed to execute systemd-firstboot")?;
-        Command::new("/usr/bin/systemd-firstboot")
-            .args(["--root", ROOT, "--keymap", &self.keymap.to_string()])
-            .status()
-            .context("Failed to execute systemd-firstboot")?;
-        Command::new("/usr/bin/systemd-firstboot")
-            .args(["--root", ROOT, "--timezone", self.timezone.as_str()])
-            .status()
-            .context("Failed to execute systemd-firstboot")?;
 
         Ok(())
     }
diff --git a/rust/package/agama-cli.changes b/rust/package/agama-cli.changes
index 074339a3f5..38b6622ad3 100644
--- a/rust/package/agama-cli.changes
+++ b/rust/package/agama-cli.changes
@@ -1,3 +1,9 @@
+-------------------------------------------------------------------
+Sun Dec  3 15:53:34 UTC 2023 - Imobach Gonzalez Sosa <igonzalezsosa@suse.com>
+
+- Use a single call to systemd-firstboot to write the localization
+  settings (gh#openSUSE/agama#903).
+
 -------------------------------------------------------------------
 Sat Dec  2 18:05:54 UTC 2023 - Imobach Gonzalez Sosa <igonzalezsosa@suse.com>
 
diff --git a/service/lib/agama/dbus/y2dir/modules/InstFunctions.rb b/service/lib/agama/dbus/y2dir/modules/InstFunctions.rb
new file mode 100644
index 0000000000..a1d5a21cc4
--- /dev/null
+++ b/service/lib/agama/dbus/y2dir/modules/InstFunctions.rb
@@ -0,0 +1,58 @@
+# Copyright (c) [2022-2023] SUSE LLC
+#
+# All Rights Reserved.
+#
+# This program is free software; you can redistribute it and/or modify it
+# under the terms of version 2 of the GNU General Public License as published
+# by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+# more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program; if not, contact SUSE LLC.
+#
+# To contact SUSE LLC about this file by physical or electronic mail, you may
+# find current contact information at www.suse.com.
+
+require "yast"
+
+# :nodoc:
+module Yast
+  # Replacement for the Yast::Package module
+  #
+  # @see https://github.com/yast/yast-installation/blob/279b7d108eab24082237cf5e3f02a31f58fef8da/src/modules/InstFunctions.rb
+  class InstFunctionsClass < Module
+    def main
+      puts "Loading mocked module #{__FILE__}"
+    end
+
+    # @see https://github.com/yast/yast-installation/blob/279b7d108eab24082237cf5e3f02a31f58fef8da/src/modules/InstFunctions.rb#L56
+    def ignored_features
+      []
+    end
+
+    # @see https://github.com/yast/yast-installation/blob/279b7d108eab24082237cf5e3f02a31f58fef8da/src/modules/InstFunctions.rb#L83
+    def reset_ignored_features; end
+
+    # @see https://github.com/yast/yast-installation/blob/279b7d108eab24082237cf5e3f02a31f58fef8da/src/modules/InstFunctions.rb#L91
+    def feature_ignored?(_feature_name)
+      false
+    end
+
+    # @see https://github.com/yast/yast-installation/blob/279b7d108eab24082237cf5e3f02a31f58fef8da/src/modules/InstFunctions.rb#L107
+    def second_stage_required?
+      false
+    end
+
+    # @see https://github.com/yast/yast-installation/blob/279b7d108eab24082237cf5e3f02a31f58fef8da/src/modules/InstFunctions.rb#L137
+    def self_update_explicitly_enabled?
+      false
+    end
+  end
+
+  InstFunctions = InstFunctionsClass.new
+  InstFunctions.main
+end
diff --git a/service/lib/agama/dbus/y2dir/storage/modules/InstFunctions.rb b/service/lib/agama/dbus/y2dir/storage/modules/InstFunctions.rb
new file mode 120000
index 0000000000..42c5d80092
--- /dev/null
+++ b/service/lib/agama/dbus/y2dir/storage/modules/InstFunctions.rb
@@ -0,0 +1 @@
+../../modules/InstFunctions.rb
\ No newline at end of file
diff --git a/service/package/rubygem-agama.changes b/service/package/rubygem-agama.changes
index 596ead89a6..ea4c958623 100644
--- a/service/package/rubygem-agama.changes
+++ b/service/package/rubygem-agama.changes
@@ -1,3 +1,10 @@
+-------------------------------------------------------------------
+Sun Dec  3 15:45:22 UTC 2023 - Imobach Gonzalez Sosa <igonzalezsosa@suse.com>
+
+- Redefine the InstFunctions module to avoid calling code that
+  causes unwanted side effects, like resetting the timezone
+  (gh#openSUSE/agama#903).
+
 -------------------------------------------------------------------
 Sat Dec  2 18:05:37 UTC 2023 - Imobach Gonzalez Sosa <igonzalezsosa@suse.com>