diff --git a/src/core/json-state-store.mjs b/src/core/json-state-store.mjs
index c688559..272e784 100644
--- a/src/core/json-state-store.mjs
+++ b/src/core/json-state-store.mjs
@@ -28,8 +28,9 @@ export function createJsonStateStore({ stateDir, fileName, initialState = {} })
 }
 
 function replaceState(target, nextState) {
+  const source = nextState === target ? structuredClone(nextState) : (nextState || {});
   for (const key of Object.keys(target)) delete target[key];
-  Object.assign(target, nextState || {});
+  Object.assign(target, source);
 }
 
 function loadState(filePath, initialState) {
diff --git a/test/json-state-store.test.mjs b/test/json-state-store.test.mjs
new file mode 100644
index 0000000..542134c
--- /dev/null
+++ b/test/json-state-store.test.mjs
@@ -0,0 +1,54 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+
+import { createJsonStateStore } from '../src/core/json-state-store.mjs';
+
+test('json state store preserves mutated in-memory state on setState', () => {
+  const stateDir = fs.mkdtempSync(path.join(os.tmpdir(), 'unrip-json-state-'));
+  const store = createJsonStateStore({
+    stateDir,
+    fileName: 'state.json',
+    initialState: {
+      paused: false,
+      publish_count: 0,
+      deposit_addresses: {},
+    },
+  });
+
+  const state = store.getState();
+  state.publish_count = 1;
+  state.deposit_addresses['btc:mainnet'] = {
+    address: 'bc1qexample',
+  };
+
+  store.setState(state);
+
+  assert.deepEqual(store.getState(), {
+    paused: false,
+    publish_count: 1,
+    deposit_addresses: {
+      'btc:mainnet': {
+        address: 'bc1qexample',
+      },
+    },
+  });
+
+  const reloaded = createJsonStateStore({
+    stateDir,
+    fileName: 'state.json',
+    initialState: {},
+  });
+
+  assert.deepEqual(reloaded.getState(), {
+    paused: false,
+    publish_count: 1,
+    deposit_addresses: {
+      'btc:mainnet': {
+        address: 'bc1qexample',
+      },
+    },
+  });
+});