diff --git a/src/handlers/cipher-full-update.ts b/src/handlers/cipher-full-update.ts
new file mode 100644
index 0000000..08c29c3
--- /dev/null
+++ b/src/handlers/cipher-full-update.ts
@@ -0,0 +1,32 @@
+interface AliasedValue<T> {
+  present: boolean;
+  value: T | null | undefined;
+}
+
+function readOwnAliasedValue<T>(source: unknown, aliases: readonly string[]): AliasedValue<T> {
+  if (!source || typeof source !== 'object') {
+    return { present: false, value: undefined };
+  }
+
+  const record = source as Record<string, unknown>;
+  for (const alias of aliases) {
+    if (Object.prototype.hasOwnProperty.call(record, alias)) {
+      return { present: true, value: record[alias] as T | null | undefined };
+    }
+  }
+
+  return { present: false, value: undefined };
+}
+
+/**
+ * Full cipher updates use replacement semantics for nullable fields.
+ * Bitwarden clients may omit a property after its value is cleared, so an
+ * absent property must become null instead of falling back to stored data.
+ */
+export function readNullableFullUpdateField<T>(
+  source: unknown,
+  aliases: readonly string[]
+): T | null {
+  const incoming = readOwnAliasedValue<T>(source, aliases);
+  return incoming.present ? incoming.value ?? null : null;
+}
diff --git a/src/handlers/ciphers.ts b/src/handlers/ciphers.ts
index 4a01420..2298433 100644
--- a/src/handlers/ciphers.ts
+++ b/src/handlers/ciphers.ts
@@ -27,6 +27,7 @@ import { deleteAllAttachmentsForCipher, deleteAllAttachmentsForCiphers } from '.
 import { parsePagination, encodeContinuationToken } from '../utils/pagination';
 import { readActingDeviceIdentifier } from '../utils/device';
 import { auditRequestMetadata, writeAuditEvent } from '../services/audit-events';
+import { readNullableFullUpdateField } from './cipher-full-update';
 
 // CONTRACT:
 // Cipher JSON is the highest-risk Bitwarden compatibility surface. Preserve
@@ -1100,16 +1101,10 @@ export async function handleUpdateCipher(request: Request, env: Env, userId: str
     cipher.passwordHistory = incomingPasswordHistory.value ?? null;
   }
 
-  // Custom fields deletion compatibility:
-  // - Accept both camelCase "fields" and PascalCase "Fields".
-  // - For full update (PUT/POST on this endpoint), missing fields means cleared fields.
-  //   This prevents stale custom fields from being resurrected by merge fallback.
-  const incomingFields = getAliasedProp(cipherData, ['fields', 'Fields']);
-  if (incomingFields.present) {
-    cipher.fields = incomingFields.value ?? null;
-  } else if (request.method === 'PUT' || request.method === 'POST') {
-    cipher.fields = null;
-  }
+  // Nullable fields use replacement semantics on this full-update endpoint.
+  // Some clients omit cleared values, so merge fallback must not resurrect them.
+  cipher.notes = readNullableFullUpdateField<string>(cipherData, ['notes', 'Notes']);
+  cipher.fields = readNullableFullUpdateField<Cipher['fields']>(cipherData, ['fields', 'Fields']);
   normalizeCipherForStorage(cipher);
   const compatibilityError = validateCipherEncryptedFieldsForCompatibility(cipher);
   if (compatibilityError) return errorResponse(compatibilityError, 400);