diff --git a/packages/protocol/src/state/AppendOnlyStateSet.ts b/packages/protocol/src/state/AppendOnlyStateSet.ts
new file mode 100644
index 000000000..ba4320641
--- /dev/null
+++ b/packages/protocol/src/state/AppendOnlyStateSet.ts
@@ -0,0 +1,64 @@
+import type { Bool, Field, FlexibleProvablePure } from "o1js";
+import { Mixin } from "ts-mixer";
+
+import { Path } from "../model/Path";
+
+import { State, WithStateServiceProvider, WithPath } from "./State";
+
+/**
+ * Map-like wrapper for state
+ */
+export class AppendOnlyStateSet<ValueType> extends Mixin(
+  WithPath,
+  WithStateServiceProvider
+) {
+  /**
+   * Create a new state map with the given key and value types
+   *
+   * @param keyType - Type to be used as a key
+   * @param valueType - Type to be stored as a value
+   * @returns State map with provided key and value types.
+   */
+  public static from<ValueType>(
+    valueType: FlexibleProvablePure<ValueType>
+  ): AppendOnlyStateSet<ValueType> {
+    return new AppendOnlyStateSet<ValueType>(valueType);
+  }
+
+  public constructor(public valueType: FlexibleProvablePure<ValueType>) {
+    super();
+  }
+
+  public getPath(value: ValueType): Field {
+    this.hasPathOrFail();
+    return Path.fromKey(this.path, this.valueType, value);
+  }
+
+  // TODO has? includes?
+  public async contains(value: ValueType): Promise<Bool> {
+    // TODO This does a unnecessary hashing step to determine the leaf value.
+    //  We would be fine with just storing a Bool here, but that means writing a
+    //  custom variant of `State`
+    const state = State.from(this.valueType);
+    this.hasPathOrFail();
+    this.hasStateServiceOrFail();
+
+    state.path = this.getPath(value);
+    state.stateServiceProvider = this.stateServiceProvider;
+    const stateValue = await state.get();
+    return stateValue.isSome;
+  }
+
+  private async add(value: ValueType): Promise<void> {
+    const state = State.from(this.valueType);
+    this.hasPathOrFail();
+    this.hasStateServiceOrFail();
+
+    state.path = this.getPath(value);
+    state.stateServiceProvider = this.stateServiceProvider;
+
+    return await state.set(value);
+  }
+
+  // TODO Adding a remove would require State.delete()
+}
diff --git a/packages/protocol/src/state/StateMap.ts b/packages/protocol/src/state/StateMap.ts
index 53fe51be4..7b2761178 100644
--- a/packages/protocol/src/state/StateMap.ts
+++ b/packages/protocol/src/state/StateMap.ts
@@ -66,7 +66,7 @@ export class StateMap<KeyType, ValueType> extends Mixin(
     this.hasPathOrFail();
     this.hasStateServiceOrFail();
 
-    state.path = Path.fromKey(this.path, this.keyType, key);
+    state.path = this.getPath(key);
     state.stateServiceProvider = this.stateServiceProvider;
     return await state.set(value);
   }