diff --git a/packages/expo-modules-core/CHANGELOG.md b/packages/expo-modules-core/CHANGELOG.md
index 47f9ea3375fc17..50a98d75addfd6 100644
--- a/packages/expo-modules-core/CHANGELOG.md
+++ b/packages/expo-modules-core/CHANGELOG.md
@@ -8,6 +8,8 @@
 
 ### 🐛 Bug fixes
 
+- [iOS] Fixed `field.options.insert()` silently failing in `fieldsOf()` due to mutation on protocol existential. ([#43341](https://github.com/expo/expo/pull/43341) by [@just1and0](https://github.com/just1and0))
+
 ### 💡 Others
 
 ## 55.0.10 — 2026-02-20
diff --git a/packages/expo-modules-core/ios/Core/Records/Record.swift b/packages/expo-modules-core/ios/Core/Records/Record.swift
index eac762bbdbe80e..c40042eca5028c 100644
--- a/packages/expo-modules-core/ios/Core/Records/Record.swift
+++ b/packages/expo-modules-core/ios/Core/Records/Record.swift
@@ -97,7 +97,7 @@ internal func fieldsOf(_ record: Record) -> [AnyFieldInternal] {
     guard var field = value as? AnyFieldInternal, let key = field.key ?? convertLabelToKey(label) else {
       return nil
     }
-    field.options.insert(.keyed(key))
+    field.options = field.options.union([.keyed(key)])
     return field
   }
 }