diff --git a/lib/protected-patterns.ts b/lib/protected-patterns.ts
index a59605bc..15d1535c 100644
--- a/lib/protected-patterns.ts
+++ b/lib/protected-patterns.ts
@@ -1,5 +1,9 @@
 function normalizePath(input: string): string {
-    return input.replaceAll("\\\\", "/")
+    // A single backslash. In source, "\\" is the one-character string; the
+    // previous "\\\\" was a *two*-character string, so it only ever matched a
+    // doubled separator -- which a real Windows path does not contain. The
+    // normalisation was therefore a no-op on the only platform that needs it.
+    return input.replaceAll("\\", "/")
 }
 
 function escapeRegExpChar(ch: string): string {
diff --git a/tests/protected-patterns.test.ts b/tests/protected-patterns.test.ts
new file mode 100644
index 00000000..49c941a1
--- /dev/null
+++ b/tests/protected-patterns.test.ts
@@ -0,0 +1,104 @@
+import assert from "node:assert/strict"
+import test from "node:test"
+import {
+    getFilePathsFromParameters,
+    isFilePathProtected,
+    isToolNameProtected,
+    matchesGlob,
+} from "../lib/protected-patterns"
+
+// A single backslash, built from its char code so the intent survives any later
+// reformatting of this file. The bug being pinned here was precisely an escaping
+// mistake in a string literal, so the tests avoid writing one by hand.
+const BS = String.fromCharCode(92)
+const winPath = (...segments: string[]) => segments.join(BS)
+
+test("matchesGlob treats a Windows separator as a path separator", () => {
+    // `protectedFilePatterns` is documented with forward slashes ("**/*.config.ts"),
+    // but on Windows the tool parameters carry backslashes. Both sides are
+    // normalised, so the same pattern must match either spelling of the same file.
+    const path = winPath("C:", "repo", "src", "config", "secrets.ts")
+
+    assert.equal(matchesGlob(path, "**/secrets.ts"), true)
+    assert.equal(matchesGlob(path, "**/config/*.ts"), true)
+    assert.equal(matchesGlob(path, "C:/repo/src/**"), true)
+    assert.equal(matchesGlob(path, "**/*.ts"), true)
+})
+
+test("matchesGlob accepts a pattern written with Windows separators", () => {
+    // Normalisation applies to the pattern too, so a user who copies a path out of
+    // Explorer and uses it as a pattern gets the same result as the documented form.
+    const pattern = winPath("**", "config", "*.ts")
+
+    assert.equal(matchesGlob("C:/repo/src/config/secrets.ts", pattern), true)
+    assert.equal(matchesGlob(winPath("C:", "repo", "src", "config", "secrets.ts"), pattern), true)
+})
+
+test("a single-segment wildcard still does not cross a Windows separator", () => {
+    // `*` is defined as "[^/]*". Normalisation must convert separators rather than
+    // erase them, or `*` would silently start matching across directories.
+    assert.equal(matchesGlob(winPath("src", "config", "secrets.ts"), "src/*"), false)
+    assert.equal(matchesGlob(winPath("src", "config", "secrets.ts"), "src/*/*.ts"), true)
+    assert.equal(matchesGlob(winPath("src", "secrets.ts"), "src/*"), true)
+})
+
+test("isFilePathProtected protects a Windows path the user configured", () => {
+    // The end-to-end shape: a `read` tool call on Windows, checked against the
+    // documented pattern style. This is the assertion that failed before the fix --
+    // the file was protected on POSIX and unprotected on Windows.
+    const patterns = ["**/secrets.ts", "**/.env"]
+
+    for (const path of [
+        "C:/repo/src/config/secrets.ts",
+        winPath("C:", "repo", "src", "config", "secrets.ts"),
+    ]) {
+        const paths = getFilePathsFromParameters("read", { filePath: path })
+        assert.equal(isFilePathProtected(paths, patterns), true, `not protected: ${path}`)
+    }
+})
+
+test("isFilePathProtected still returns false for a genuinely unmatched path", () => {
+    // The fix must widen matching only for separators, not for anything else.
+    const paths = getFilePathsFromParameters("read", {
+        filePath: winPath("C:", "repo", "src", "main.ts"),
+    })
+
+    assert.equal(isFilePathProtected(paths, ["**/secrets.ts"]), false)
+    assert.equal(isFilePathProtected(paths, []), false)
+    assert.equal(isFilePathProtected([], ["**/*.ts"]), false)
+})
+
+test("multiedit and apply_patch paths are protected on Windows too", () => {
+    // These two tools carry paths in shapes of their own, so they need their own
+    // coverage: a nested `edits` array and paths embedded in patch text.
+    const patterns = ["**/secrets.ts"]
+
+    const multiedit = getFilePathsFromParameters("multiedit", {
+        filePath: winPath("src", "main.ts"),
+        edits: [{ filePath: winPath("src", "config", "secrets.ts") }],
+    })
+    assert.equal(isFilePathProtected(multiedit, patterns), true)
+
+    const patch = getFilePathsFromParameters("apply_patch", {
+        patchText: `*** Update File: ${winPath("src", "config", "secrets.ts")}\n@@\n-a\n+b\n`,
+    })
+    assert.equal(isFilePathProtected(patch, patterns), true)
+})
+
+test("isToolNameProtected is unaffected by separator normalisation", () => {
+    // Tool names contain no separators; this pins that the shared helper does not
+    // change their behaviour.
+    assert.equal(isToolNameProtected("bash", ["bash"]), true)
+    assert.equal(isToolNameProtected("bash", ["ba*"]), true)
+    assert.equal(isToolNameProtected("bash", ["read"]), false)
+    assert.equal(isToolNameProtected("bash", []), false)
+    assert.equal(isToolNameProtected("", ["bash"]), false)
+})
+
+test("matchesGlob rejects an empty pattern and handles regex metacharacters", () => {
+    // Pattern text is interpolated into a RegExp, so characters that mean something
+    // there must be matched literally.
+    assert.equal(matchesGlob("a/b.ts", ""), false)
+    assert.equal(matchesGlob("src/a+b(1).ts", "src/a+b(1).ts"), true)
+    assert.equal(matchesGlob("src/axb1.ts", "src/a+b(1).ts"), false)
+})