diff --git a/web/src/wasm-core.js b/web/src/wasm-core.js
index 339cf3d..612e3a6 100644
--- a/web/src/wasm-core.js
+++ b/web/src/wasm-core.js
@@ -713,7 +713,7 @@ export async function createWasmSimulator(moduleOptions = {}) {
         // through the WASM mirror, so preserve the loaded OPFS file here.
         if (previousParameterFile === null) {
           await opfs.removeFile(`${parameterPath}.bak`);
-        } else if (!(await opfs.exists(`${parameterPath}.bak`))) {
+        } else {
           await opfs.writeFile(`${parameterPath}.bak`, previousParameterFile);
         }
         return events;
diff --git a/web/test-browser-wasm-smoke-opfs-parameter-sections.js b/web/test-browser-wasm-smoke-opfs-parameter-sections.js
index b3e0300..e486809 100644
--- a/web/test-browser-wasm-smoke-opfs-parameter-sections.js
+++ b/web/test-browser-wasm-smoke-opfs-parameter-sections.js
@@ -93,9 +93,10 @@ export async function runBrowserOpfsParameterSections(context, simulator) {
 
   await runSection("opfs parameter backup after existing save", async () => {
     await simulator.fs.opfs.writeFile("parameters/existing-save.var", "5161\t3.000000\n");
-    // LinuxCNC source basis: rs274ngc_pre.cc save_parameters()
-    // unlinks filename + ".bak", links the current parameter file to
-    // filename + ".bak", then renames filename + ".new" over filename.
+    await simulator.fs.opfs.writeFile("parameters/existing-save.var.bak", "stale previous backup\n");
+    // LinuxCNC source basis: rs274ngc_pre.cc save_parameters() unlinks
+    // filename + ".bak", links the current parameter file to it,
+    // then renames filename + ".new" over filename.
     await simulator.parseWithParameterFile(
       "G21 G90\nG0 X4\nG28.1\nM30\n",
       "parameters/existing-save.var",
@@ -103,11 +104,9 @@ export async function runBrowserOpfsParameterSections(context, simulator) {
       backend,
     );
     const existingSaveParameterFile = await readOpfsText(simulator, "parameters/existing-save.var");
-    expectIncludes(existingSaveParameterFile, "5161\t4.000000",
-      "LinuxCNC existing OPFS parameter file was not replaced after save");
+    expectIncludes(existingSaveParameterFile, "5161\t4.000000", "LinuxCNC existing OPFS parameter file was not replaced after save");
     const existingSaveParameterBackup = await readOpfsText(simulator, "parameters/existing-save.var.bak");
-    expectIncludes(existingSaveParameterBackup, "5161\t3.000000",
-      "LinuxCNC existing OPFS parameter backup did not preserve the previous file");
+    expectIncludes(existingSaveParameterBackup, "5161\t3.000000", "LinuxCNC existing OPFS parameter backup did not replace the stale backup with the previous file");
     await expectMissingOpfsFile(
       () => simulator.fs.opfs.readFile("parameters/existing-save.var.new"),
       "LinuxCNC existing OPFS parameter temporary file remained after save",