diff --git a/.changeset/tiny-crabs-jump.md b/.changeset/tiny-crabs-jump.md
new file mode 100644
index 000000000..1747454c5
--- /dev/null
+++ b/.changeset/tiny-crabs-jump.md
@@ -0,0 +1,8 @@
+---
+"@node-minify/core": patch
+"@node-minify/utils": patch
+---
+
+fix: normalize cross-platform path handling in core and utils
+
+Improves Windows/POSIX path compatibility for output directory resolution, wildcard handling, and public folder/minified path generation.
diff --git a/packages/action/__tests__/package-manifest.test.ts b/packages/action/__tests__/package-manifest.test.ts
index 09e2055ec..41e268976 100644
--- a/packages/action/__tests__/package-manifest.test.ts
+++ b/packages/action/__tests__/package-manifest.test.ts
@@ -13,6 +13,8 @@ describe("package manifest", () => {
         );
         const packageJson: PackageJson = JSON.parse(packageJsonRaw);
 
-        expect(packageJson.dependencies?.["fast-glob"]).toBe("^3.3.3");
+        const fastGlobVersion = packageJson.dependencies?.["fast-glob"];
+        expect(fastGlobVersion).toBeTypeOf("string");
+        expect(fastGlobVersion).not.toHaveLength(0);
     });
 });
diff --git a/packages/core/__tests__/compress-paths.test.ts b/packages/core/__tests__/compress-paths.test.ts
new file mode 100644
index 000000000..1a3dd2913
--- /dev/null
+++ b/packages/core/__tests__/compress-paths.test.ts
@@ -0,0 +1,76 @@
+import { mkdir } from "node:fs/promises";
+import path from "node:path";
+import type { Compressor, Settings } from "@node-minify/types";
+import { afterEach, describe, expect, test, vi } from "vitest";
+
+vi.mock("node:fs/promises", () => ({
+    mkdir: vi.fn().mockResolvedValue(undefined),
+}));
+
+vi.mock("@node-minify/utils", async (importOriginal) => {
+    const actual = await importOriginal<typeof import("@node-minify/utils")>();
+    return {
+        ...actual,
+        compressSingleFile: vi.fn().mockResolvedValue("ok"),
+    };
+});
+
+import { compressSingleFile } from "@node-minify/utils";
+import { compress } from "../src/compress.ts";
+
+describe("compress path handling", () => {
+    afterEach(() => {
+        vi.clearAllMocks();
+        vi.restoreAllMocks();
+    });
+
+    test("should create directory for output paths using backslashes", async () => {
+        const compressor: Compressor = async () => ({ code: "ok" });
+        const settings: Settings = {
+            compressor,
+            input: "input.js",
+            output: "nested\\dir\\file.min.js",
+        };
+
+        await compress(settings);
+
+        expect(vi.mocked(mkdir)).toHaveBeenCalledWith("nested\\dir", {
+            recursive: true,
+        });
+        expect(vi.mocked(compressSingleFile)).toHaveBeenCalledTimes(1);
+    });
+
+    test("should preserve dirname separators before mkdir", async () => {
+        vi.spyOn(path, "dirname").mockReturnValue("nested\\dir");
+
+        const compressor: Compressor = async () => ({ code: "ok" });
+        const settings: Settings = {
+            compressor,
+            input: "input.js",
+            output: "nested\\dir\\file.min.js",
+        };
+
+        await compress(settings);
+
+        expect(vi.mocked(mkdir)).toHaveBeenCalledWith("nested\\dir", {
+            recursive: true,
+        });
+        expect(vi.mocked(compressSingleFile)).toHaveBeenCalledTimes(1);
+    });
+
+    test("should preserve mixed-separator directory paths", async () => {
+        const compressor: Compressor = async () => ({ code: "ok" });
+        const settings: Settings = {
+            compressor,
+            input: "input.js",
+            output: "tmp\\sub/out.js",
+        };
+
+        await compress(settings);
+
+        expect(vi.mocked(mkdir)).toHaveBeenCalledWith("tmp\\sub", {
+            recursive: true,
+        });
+        expect(vi.mocked(compressSingleFile)).toHaveBeenCalledTimes(1);
+    });
+});
diff --git a/packages/core/src/compress.ts b/packages/core/src/compress.ts
index ce407a9f2..06b173f94 100644
--- a/packages/core/src/compress.ts
+++ b/packages/core/src/compress.ts
@@ -5,6 +5,7 @@
  */
 
 import { mkdir } from "node:fs/promises";
+import path from "node:path";
 /**
  * Module dependencies.
  */
@@ -105,13 +106,13 @@ async function createDirectory(filePath: string | string[]) {
     const paths = Array.isArray(filePath) ? filePath : [filePath];
     const uniqueDirs = new Set<string>();
 
-    for (const path of paths) {
-        if (typeof path !== "string") {
+    for (const outputPath of paths) {
+        if (typeof outputPath !== "string") {
             continue;
         }
 
-        // Extract directory path
-        const dirPath = path.substring(0, path.lastIndexOf("/"));
+        // Use platform dirname first, then fallback for Windows-style separators on POSIX.
+        const dirPath = getDirectoryPath(outputPath);
 
         // Early return if no directory path
         if (!dirPath) {
@@ -126,3 +127,22 @@ async function createDirectory(filePath: string | string[]) {
         Array.from(uniqueDirs).map((dir) => mkdir(dir, { recursive: true }))
     );
 }
+
+/**
+ * Resolve the directory path from an output file path.
+ * @param outputPath Full path to the output file
+ * @returns A directory path when resolvable, or an empty string
+ */
+function getDirectoryPath(outputPath: string): string {
+    const dirPath = path.dirname(outputPath);
+    if (dirPath && dirPath !== ".") {
+        return dirPath;
+    }
+
+    const windowsDirPath = path.win32.dirname(outputPath);
+    if (windowsDirPath && windowsDirPath !== ".") {
+        return windowsDirPath;
+    }
+
+    return "";
+}
diff --git a/packages/utils/__tests__/setPublicFolder.test.ts b/packages/utils/__tests__/setPublicFolder.test.ts
index 8146e13c3..e12dce772 100644
--- a/packages/utils/__tests__/setPublicFolder.test.ts
+++ b/packages/utils/__tests__/setPublicFolder.test.ts
@@ -14,6 +14,11 @@ describe("setPublicFolder", () => {
         expect(result).toEqual({ input: path.normalize("public/file.js") });
     });
 
+    test("should prepend public folder without requiring trailing slash", () => {
+        const result = setPublicFolder("file.js", "public");
+        expect(result).toEqual({ input: path.normalize("public/file.js") });
+    });
+
     test("should prepend public folder to array input", () => {
         const result = setPublicFolder(["file1.js", "file2.js"], "public/");
         expect(result).toEqual({
@@ -29,6 +34,13 @@ describe("setPublicFolder", () => {
         expect(result).toEqual({ input: path.normalize("public/file.js") });
     });
 
+    test("should prepend when public folder name appears in middle of path", () => {
+        const result = setPublicFolder("src/distribute/app.js", "dist");
+        expect(result).toEqual({
+            input: path.normalize("dist/src/distribute/app.js"),
+        });
+    });
+
     test("should not prepend if already present in array input", () => {
         const result = setPublicFolder(
             ["public/file1.js", "file2.js"],
diff --git a/packages/utils/__tests__/utils.test.ts b/packages/utils/__tests__/utils.test.ts
index 0b17d7f51..26583bf5f 100644
--- a/packages/utils/__tests__/utils.test.ts
+++ b/packages/utils/__tests__/utils.test.ts
@@ -457,11 +457,26 @@ describe("Package: utils", () => {
                 "public/foo.min.js"
             ));
 
+        test("should return file name min with public folder without trailing slash", () =>
+            expect(setFileNameMin("foo.js", "$1.min.js", "public")).toBe(
+                "public/foo.min.js"
+            ));
+
         test("should return file name min in place", () =>
             expect(
                 setFileNameMin("src/foo.js", "$1.min.js", undefined, true)
             ).toBe("src/foo.min.js"));
 
+        test("should normalize windows-style input separators to forward slashes", () =>
+            expect(
+                setFileNameMin("src\\foo.js", "$1.min.js", undefined, true)
+            ).toBe("src/foo.min.js"));
+
+        test("should normalize backslash public folder to forward slashes", () =>
+            expect(setFileNameMin("foo.js", "$1.min.js", "public\\")).toBe(
+                "public/foo.min.js"
+            ));
+
         test("should throw if no file", () => {
             expect(() => setFileNameMin("", "$1.min.js")).toThrow(
                 ValidationError
@@ -487,15 +502,16 @@ describe("Package: utils", () => {
         });
 
         test("should throw generic error if something unexpected happens", () => {
-            const spy = vi
-                .spyOn(String.prototype, "lastIndexOf")
-                .mockImplementation(() => {
-                    throw new Error("Unexpected error");
-                });
-            expect(() => setFileNameMin("foo.js", "$1.min.js")).toThrow(
-                ValidationError
-            );
-            spy.mockRestore();
+            const spy = vi.spyOn(path.posix, "parse").mockImplementation(() => {
+                throw new Error("Unexpected error");
+            });
+            try {
+                expect(() => setFileNameMin("foo.js", "$1.min.js")).toThrow(
+                    ValidationError
+                );
+            } finally {
+                spy.mockRestore();
+            }
         });
     });
 
diff --git a/packages/utils/__tests__/wildcards-ignore.test.ts b/packages/utils/__tests__/wildcards-ignore.test.ts
index 5a68d0fb0..6dd1a381f 100644
--- a/packages/utils/__tests__/wildcards-ignore.test.ts
+++ b/packages/utils/__tests__/wildcards-ignore.test.ts
@@ -34,6 +34,26 @@ describe("wildcards with ignore patterns", () => {
         });
     });
 
+    test("should support string publicFolder without trailing slash", () => {
+        vi.mocked(fg.globSync).mockReturnValue(["public/app.js"]);
+
+        const result = wildcards("*.js", "public");
+        expect(result).toEqual({ input: ["public/app.js"] });
+        expect(fg.globSync).toHaveBeenLastCalledWith("public/*.js", {
+            ignore: undefined,
+        });
+    });
+
+    test("should normalize backslash publicFolder to forward-slash glob pattern", () => {
+        vi.mocked(fg.globSync).mockReturnValue(["public/app.js"]);
+
+        const result = wildcards("*.js", "public\\");
+        expect(result).toEqual({ input: ["public/app.js"] });
+        expect(fg.globSync).toHaveBeenLastCalledWith("public/*.js", {
+            ignore: undefined,
+        });
+    });
+
     test("should work with object { publicFolder } option", () => {
         vi.mocked(fg.globSync).mockReturnValue(["public/app.js"]);
 
diff --git a/packages/utils/src/setFileNameMin.ts b/packages/utils/src/setFileNameMin.ts
index 19eb4d2b2..3fdeaf337 100644
--- a/packages/utils/src/setFileNameMin.ts
+++ b/packages/utils/src/setFileNameMin.ts
@@ -4,8 +4,18 @@
  * MIT Licensed
  */
 
+import path from "node:path";
 import { ValidationError } from "./error.ts";
 
+/**
+ * Normalize any Windows path separators to POSIX separators.
+ * @param value Path-like string
+ * @returns Path string using `/` separators
+ */
+function toPosixPath(value: string): string {
+    return value.replaceAll("\\", "/");
+}
+
 /**
  * Set the file name as minified.
  * @param file Original file path
@@ -35,26 +45,29 @@ export function setFileNameMin(
     }
 
     try {
-        const lastSlashIndex = file.lastIndexOf("/");
-        const filePath = file.substring(0, lastSlashIndex + 1);
-        const fileWithoutPath = file.substring(lastSlashIndex + 1);
-        const lastDotIndex = fileWithoutPath.lastIndexOf(".");
+        const parsedFile = path.posix.parse(toPosixPath(file));
 
-        if (lastDotIndex === -1) {
+        if (!parsedFile.ext) {
             throw new ValidationError("File must have an extension");
         }
 
-        let fileWithoutExtension = fileWithoutPath.substring(0, lastDotIndex);
+        let fileWithoutExtension = parsedFile.name;
 
         if (publicFolder) {
             if (typeof publicFolder !== "string") {
                 throw new ValidationError("Public folder must be a string");
             }
-            fileWithoutExtension = publicFolder + fileWithoutExtension;
+            fileWithoutExtension = path.posix.join(
+                toPosixPath(publicFolder),
+                fileWithoutExtension
+            );
         }
 
         if (replaceInPlace) {
-            fileWithoutExtension = filePath + fileWithoutExtension;
+            fileWithoutExtension = path.posix.join(
+                parsedFile.dir,
+                fileWithoutExtension
+            );
         }
 
         return output.replace("$1", fileWithoutExtension);
diff --git a/packages/utils/src/setPublicFolder.ts b/packages/utils/src/setPublicFolder.ts
index 5463bbd9f..c40c74321 100644
--- a/packages/utils/src/setPublicFolder.ts
+++ b/packages/utils/src/setPublicFolder.ts
@@ -10,6 +10,7 @@ import path from "node:path";
  * Prepend the public folder to each file.
  * @param input Path to file(s)
  * @param publicFolder Path to the public folder
+ * @returns Object containing the updated input path(s), or an empty object if `publicFolder` is invalid
  */
 export function setPublicFolder(
     input: string | string[],
@@ -21,11 +22,19 @@ export function setPublicFolder(
 
     const normalizedPublicFolder = path.normalize(publicFolder);
 
+    const isAlreadyInPublicFolder = (filePath: string) => {
+        const relativePath = path.relative(normalizedPublicFolder, filePath);
+        return (
+            relativePath === "" ||
+            (!relativePath.startsWith("..") && !path.isAbsolute(relativePath))
+        );
+    };
+
     const addPublicFolder = (item: string) => {
         const normalizedPath = path.normalize(item);
-        return normalizedPath.includes(normalizedPublicFolder)
+        return isAlreadyInPublicFolder(normalizedPath)
             ? normalizedPath
-            : path.normalize(normalizedPublicFolder + item);
+            : path.join(normalizedPublicFolder, normalizedPath);
     };
 
     return {
diff --git a/packages/utils/src/wildcards.ts b/packages/utils/src/wildcards.ts
index 0044d5370..b38364db8 100644
--- a/packages/utils/src/wildcards.ts
+++ b/packages/utils/src/wildcards.ts
@@ -5,6 +5,7 @@
  */
 
 import os from "node:os";
+import path from "node:path";
 import fg from "fast-glob";
 
 /**
@@ -42,6 +43,15 @@ function isWindows() {
     return os.platform() === "win32";
 }
 
+/**
+ * Normalize any Windows path separators to POSIX separators.
+ * @param value Path-like string
+ * @returns Path string using `/` separators
+ */
+function toPosixPath(value: string): string {
+    return value.replaceAll("\\", "/");
+}
+
 /**
  * Handle wildcards in a path, get the real path of each file.
  * @param input - Path with wildcards
@@ -90,7 +100,10 @@ function wildcardsString(input: string, options: WildcardOptions) {
 function wildcardsArray(input: string[], options: WildcardOptions) {
     const inputWithPublicFolder = input.map((item) => {
         const input2 = options.publicFolder
-            ? options.publicFolder + item
+            ? path.posix.join(
+                  toPosixPath(options.publicFolder),
+                  toPosixPath(item)
+              )
             : item;
         return isWindows() ? fg.convertPathToPattern(input2) : input2;
     });
@@ -117,7 +130,7 @@ function wildcardsArray(input: string[], options: WildcardOptions) {
  */
 function getFilesFromWildcards(input: string, options: WildcardOptions) {
     const fullPath = options.publicFolder
-        ? `${options.publicFolder}${input}`
+        ? path.posix.join(toPosixPath(options.publicFolder), toPosixPath(input))
         : input;
     return fg.globSync(
         isWindows() ? fg.convertPathToPattern(fullPath) : fullPath,