diff --git a/backend/src/routes/admin.module-load.test.js b/backend/src/routes/admin.module-load.test.js
new file mode 100644
index 0000000..421ffd5
--- /dev/null
+++ b/backend/src/routes/admin.module-load.test.js
@@ -0,0 +1,67 @@
+const { describe, it } = require('node:test');
+const assert = require('node:assert');
+
+/**
+ * Regression test for issue #559:
+ * Duplicate `const IMPERSONATION_TTL_SECONDS` declaration caused a
+ * SyntaxError at module load time, crashing all admin routes.
+ *
+ * This test ensures the admin router module can be required without
+ * throwing any syntax or initialization errors.
+ */
+describe('Admin Module Load (issue #559)', () => {
+  it('should require admin.js without SyntaxError', () => {
+    // If there is a duplicate const declaration, require() will throw:
+    //   SyntaxError: Identifier 'IMPERSONATION_TTL_SECONDS' has already been declared
+    try {
+      // Clear module cache to ensure we re-evaluate admin.js from scratch
+      delete require.cache[require.resolve('./admin')];
+      require('./admin');
+    } catch (err) {
+      if (err instanceof SyntaxError) {
+        assert.fail(
+          `admin.js threw SyntaxError on load — likely a duplicate const declaration: ${err.message}`
+        );
+      }
+      // MODULE_NOT_FOUND or other runtime errors are expected in isolated tests
+    }
+    // If we get here without a SyntaxError, the module loaded successfully
+  });
+
+  it('should not redeclare constants already imported from config/constants', () => {
+    const fs = require('fs');
+    const path = require('path');
+
+    const adminSource = fs.readFileSync(
+      path.join(__dirname, 'admin.js'),
+      'utf-8'
+    );
+
+    // Find all const declarations of IMPERSONATION_TTL_SECONDS
+    const constDeclarations = adminSource.match(
+      /(?:const|let|var)\s+(?:\{[^}]*\bIMPERSONATION_TTL_SECONDS\b[^}]*\}|\bIMPERSONATION_TTL_SECONDS\b)\s*=/g
+    );
+
+    assert.ok(constDeclarations, 'Should find at least one const declaration');
+
+    // There should be exactly one declaration (the destructured import from constants.js)
+    const destructuredImports = constDeclarations.filter((d) =>
+      d.includes('{')
+    );
+    assert.strictEqual(
+      destructuredImports.length,
+      1,
+      `Expected exactly 1 destructured import of IMPERSONATION_TTL_SECONDS, found ${destructuredImports.length}: ${constDeclarations}`
+    );
+
+    // Ensure no standalone `const IMPERSONATION_TTL_SECONDS =` (without destructuring)
+    const standaloneDeclarations = constDeclarations.filter(
+      (d) => !d.includes('{')
+    );
+    assert.strictEqual(
+      standaloneDeclarations.length,
+      0,
+      `Found standalone const IMPERSONATION_TTL_SECONDS declaration(s) which would shadow the import — remove them`
+    );
+  });
+});