diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7c5a500e..04e7a24b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,6 +19,7 @@ Format based on [Keep a Changelog](https://keepachangelog.com/).
 - **Product types as Bill-of-Materials components** *(admin)* — a BOM line can now be a manufactured **product type** (a sub-assembly), not only a material. In the BOM editor a Material / Product type switch picks the component kind; product-type lines carry the same quantity-per-unit, step, scrap %, consumption timing and notes as materials. A product type can't be a component of itself, and each appears once per template. Lines are captured in the work-order snapshot as sub-assembly references; they're a simple component reference (they don't explode into their own BOM) and are skipped by the material stock/consumption engine. Additive — existing material BOMs are unaffected.
 
 ### Fixed
+- **Saving system settings crashed on PostgreSQL** *(admin)* — the plant-timezone save wrote the raw identifier (e.g. `Europe/Warsaw`) into the JSON `system_settings.value` column, which PostgreSQL rejects (`invalid input syntax for type json`), 500-ing the whole Settings → System save; SQLite tolerated it, so tests missed it. The value is now JSON-encoded (and decoded on read, tolerating legacy raw values).
 - **Header clock ignored the configured timezone** *(all users)* — the live clock top-right was hardcoded to `Europe/Warsaw`, so on any install with a different timezone it was the one timestamp in the UI that disagreed with all the others. It now goes through the same `formatDate`/`formatTime` helpers as the rest of the app.
 
 ## [0.21.0] - 2026-08-21
diff --git a/backend/app/Support/TimezoneRegistry.php b/backend/app/Support/TimezoneRegistry.php
index 8642a2e6..e2f52137 100644
--- a/backend/app/Support/TimezoneRegistry.php
+++ b/backend/app/Support/TimezoneRegistry.php
@@ -59,11 +59,21 @@ public static function stored(): ?string
             return null;
         }
 
-        if (! $row || ! self::isValid((string) $row->value)) {
+        if (! $row) {
             return null;
         }
 
-        return self::$cached = (string) $row->value;
+        // `system_settings.value` is a JSON column, so the stored value is
+        // JSON-encoded (e.g. "Europe/Warsaw"). Decode it; tolerate a legacy raw
+        // string too.
+        $decoded = json_decode((string) $row->value, true);
+        $value = is_string($decoded) ? $decoded : (string) $row->value;
+
+        if (! self::isValid($value)) {
+            return null;
+        }
+
+        return self::$cached = $value;
     }
 
     /**
@@ -95,7 +105,9 @@ public static function save(string $timezone): void
 
         DB::table('system_settings')->updateOrInsert(
             ['key' => self::SETTING_KEY],
-            ['value' => $timezone, 'updated_at' => now()],
+            // JSON-encode: `value` is a JSON column, so a bare string is rejected
+            // by Postgres (works on SQLite, which is why tests missed it).
+            ['value' => json_encode($timezone), 'updated_at' => now()],
         );
 
         self::$cached = $timezone;
diff --git a/backend/tests/Feature/Web/SystemSettingsTimezoneTest.php b/backend/tests/Feature/Web/SystemSettingsTimezoneTest.php
index a1bab99a..468c6647 100644
--- a/backend/tests/Feature/Web/SystemSettingsTimezoneTest.php
+++ b/backend/tests/Feature/Web/SystemSettingsTimezoneTest.php
@@ -66,12 +66,14 @@ public function test_admin_can_change_the_plant_timezone(): void
             ->post('/settings/system', $this->payload(['app_timezone' => 'America/Argentina/Buenos_Aires']))
             ->assertSessionHasNoErrors();
 
-        // Stored raw, not JSON-encoded — TimezoneRegistry reads it as a plain
-        // identifier, so an accidental json_encode() here would break `stored()`.
+        // `system_settings.value` is a JSON column, so the identifier must be
+        // JSON-encoded — a bare string is rejected by Postgres (SQLite tolerates
+        // it, which is how the bug shipped). stored() decodes it back.
         $this->assertDatabaseHas('system_settings', [
             'key' => TimezoneRegistry::SETTING_KEY,
-            'value' => 'America/Argentina/Buenos_Aires',
+            'value' => json_encode('America/Argentina/Buenos_Aires'),
         ]);
+        TimezoneRegistry::flush();
         $this->assertSame('America/Argentina/Buenos_Aires', TimezoneRegistry::stored());
     }