diff --git a/src/Integrations/Divi/Design/SnapshotStore.php b/src/Integrations/Divi/Design/SnapshotStore.php
index 7fa208b..5ddff26 100644
--- a/src/Integrations/Divi/Design/SnapshotStore.php
+++ b/src/Integrations/Divi/Design/SnapshotStore.php
@@ -38,11 +38,16 @@ class SnapshotStore
     /**
      * @param array<array-key, mixed> $data The area's raw inventory.
      * @throws SnapshotTooLarge
-     * @throws RuntimeException When the option could not be written.
+     * @throws RuntimeException When the snapshot cannot be encoded or the option could not be written.
      */
     public function save(string $area, array $data, string $ability): string
     {
-        $size = strlen((string) wp_json_encode($data, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES));
+        $json = wp_json_encode($data, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES);
+        if (! is_string($json)) {
+            throw new RuntimeException(sprintf('snapshot %s could not be encoded', $area));
+        }
+
+        $size = strlen($json);
         if ($size > self::MAX_BYTES) {
             throw new SnapshotTooLarge($size);
         }
diff --git a/tests/Unit/Integrations/Divi/Design/SnapshotStoreTest.php b/tests/Unit/Integrations/Divi/Design/SnapshotStoreTest.php
index 2ea67a4..1d30d46 100644
--- a/tests/Unit/Integrations/Divi/Design/SnapshotStoreTest.php
+++ b/tests/Unit/Integrations/Divi/Design/SnapshotStoreTest.php
@@ -87,6 +87,25 @@ final class SnapshotStoreTest extends TestCase
         (new SnapshotStore())->save('presets', ['a' => 1], 'lit/divi-presets-set');
     }
 
+    public function testAnUnencodableSnapshotIsRefusedBeforeAnyWrite(): void
+    {
+        Functions\when('wp_json_encode')->justReturn(false);
+        $written = false;
+        Functions\when('update_option')->alias(function () use (&$written): bool {
+            $written = true;
+
+            return true;
+        });
+
+        try {
+            (new SnapshotStore())->save('presets', ['a' => 1], 'lit/divi-presets-set');
+            self::fail('an unencodable snapshot must be refused');
+        } catch (RuntimeException $e) {
+            self::assertSame('snapshot presets could not be encoded', $e->getMessage());
+        }
+        self::assertFalse($written, 'nothing may be written when the snapshot cannot be encoded');
+    }
+
     public function testCorruptOptionReadsAsEmpty(): void
     {
         $this->options['lit_mcp_snapshots_presets'] = 'kaputt';