diff --git a/dist/index.js b/dist/index.js
index 43034a7..601bcb6 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -82166,15 +82166,15 @@ var require_versions = __commonJS({
         x64: "x86_64"
       }[arch];
       const host = `${resolvedArch}-${resolvedOs}`;
-      const index = await getJSON({ url: "https://ziglang.org/download/index.json" });
-      const availableVersions = Object.keys(index);
+      const machIndex = await getJSON({ url: "https://machengine.org/zig/index.json" });
+      const availableVersions = Object.keys(machIndex);
       const useVersion = semver2.valid(version3) ? semver2.maxSatisfying(availableVersions.filter((v) => semver2.valid(v)), version3) : null;
-      const meta = index[useVersion || version3];
+      const meta = machIndex[useVersion || version3] || (await getJSON({ url: "https://ziglang.org/download/index.json" }))[useVersion || version3];
       if (!meta || !meta[host]) {
         throw new Error(`Could not find version ${useVersion || version3} for platform ${host}`);
       }
       const downloadUrl = meta[host].tarball;
-      const variantName = path2.basename(meta[host].tarball).replace(`.${ext}`, "");
+      const variantName = path2.basename(meta[host].tarball).replace(`.${ext}`, "").replace(/\+\S*$/, "");
       return { downloadUrl, variantName, version: useVersion || version3 };
     }
     __name(resolveVersion2, "resolveVersion");
@@ -82225,6 +82225,7 @@ async function downloadZig(arch, platform, version3, useCache = true) {
   actions.info(`no cached version found. downloading zig ${variantName}`);
   const downloadPath = await toolCache.downloadTool(downloadUrl);
   const zigPath = ext === "zip" ? await toolCache.extractZip(downloadPath) : await toolCache.extractTar(downloadPath, void 0, "x");
+  actions.info(`${variantName} zig downloaded and extracted to ${zigPath}`);
   const binPath = path.join(zigPath, fileWithoutFileType);
   const cachePath = await toolCache.cacheDir(binPath, TOOL_NAME, useVersion);
   if (useCache) {
diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..ad157bd
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,60 @@
+{
+  "nodes": {
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1710146030,
+        "narHash": "sha256-SZ5L6eA7HJ/nmkzGG7/ISclqe6oZdOZTNoesiInkXPQ=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "b1d9ab70662946ef0850d488da1c9019f3a9752a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1714245158,
+        "narHash": "sha256-9P2M0+tf1TE7Z5PwDVwhheuD2mFf6/phPr0Jvl7cxcc=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "2b1f64b358f2cab62617f26b3870fd0ee375d848",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "ref": "nixpkgs-unstable",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/index.js b/index.js
index 4f4c900..a62212f 100644
--- a/index.js
+++ b/index.js
@@ -49,6 +49,7 @@ async function downloadZig (arch, platform, version, useCache = true) {
     ? await toolCache.extractZip(downloadPath)
     : await toolCache.extractTar(downloadPath, undefined, 'x')
 
+  actions.info(`${variantName} zig downloaded and extracted to ${zigPath}`)
   const binPath = path.join(zigPath, fileWithoutFileType)
   const cachePath = await toolCache.cacheDir(binPath, TOOL_NAME, useVersion)
 
diff --git a/test.js b/test.js
index 81c5c35..7418d53 100644
--- a/test.js
+++ b/test.js
@@ -45,6 +45,29 @@ async function test () {
     variantName: 'zig-macos-aarch64-0.11.0',
     version: '0.11.0'
   })
+  assert.deepEqual(await resolveVersion('arm64', 'darwin', '2024.1.0-mach'), {
+    downloadUrl: 'https://pkg.machengine.org/zig/zig-macos-aarch64-0.12.0-dev.2063+804cee3b9.tar.xz',
+    variantName: 'zig-macos-aarch64-0.12.0-dev.2063',
+    version: '2024.1.0-mach'
+  })
+  assert.deepEqual(await resolveVersion('x64', 'linux', '2024.3.0-mach'), {
+    downloadUrl: 'https://pkg.machengine.org/zig/zig-linux-x86_64-0.12.0-dev.3180+83e578a18.tar.xz',
+    variantName: 'zig-linux-x86_64-0.12.0-dev.3180',
+    version: '2024.3.0-mach'
+  })
+  assert.deepEqual(await resolveVersion('x64', 'win32', '2024.1.0-mach'), {
+    downloadUrl: 'https://pkg.machengine.org/zig/zig-windows-x86_64-0.12.0-dev.2063+804cee3b9.zip',
+    variantName: 'zig-windows-x86_64-0.12.0-dev.2063',
+    version: '2024.1.0-mach'
+  })
+  assert.deepEqual(await resolveVersion('arm64', 'darwin', '2024.3.0-mach'), {
+    downloadUrl: 'https://pkg.machengine.org/zig/zig-macos-aarch64-0.12.0-dev.3180+83e578a18.tar.xz',
+    variantName: 'zig-macos-aarch64-0.12.0-dev.3180',
+    version: '2024.3.0-mach'
+  })
+  await assert.doesNotReject(resolveVersion('x64', 'linux', 'mach-latest'))
+  await assert.doesNotReject(resolveVersion('x64', 'win32', 'mach-latest'))
+  await assert.doesNotReject(resolveVersion('arm64', 'darwin', 'mach-latest'))
   await assert.doesNotReject(resolveVersion('x64', 'linux', 'master'))
   await assert.doesNotReject(resolveVersion('x64', 'win32', 'master'))
   await assert.doesNotReject(resolveVersion('arm64', 'darwin', 'master'))
diff --git a/versions.js b/versions.js
index ad91fc9..019cf4c 100644
--- a/versions.js
+++ b/versions.js
@@ -10,6 +10,12 @@ function extForPlatform (platform) {
   }[platform]
 }
 
+/**
+  * resolveCommit resolves a specific commit, so is only used
+  * in cases where the zig version is specified through the use of a plus
+  * sign. It does not require any fetch from an external resource as the
+  * data (downloadUrl, etc) can be resolved directly
+  */
 function resolveCommit (arch, platform, version) {
   const ext = extForPlatform(platform)
   const resolvedOs = {
@@ -27,6 +33,11 @@ function resolveCommit (arch, platform, version) {
   }[arch]
 
   const downloadUrl = `https://ziglang.org/builds/zig-${resolvedOs}-${resolvedArch}-${version}.${ext}`
+  // This function is only called if the version includes a '+' sign, so mach versions
+  // will not come through here
+  //
+  // Mach builds come from pkg.machengine.org
+  // const machDownloadUrl = `https://pkg.machengine.org/zig/zig-${resolvedOs}-${resolvedArch}-${version}.${ext}`
   const versionWithoutBuildHash = semver.clean(version)
   const fileWithoutFileType = `zig-${resolvedOs}-${resolvedArch}-${version}`
   const variantName = `zig-${resolvedOs}-${resolvedArch}-${versionWithoutBuildHash}`
@@ -51,6 +62,16 @@ function getJSON (opts) {
   })
 }
 
+/**
+  * resolveVersion resolves a generic commit, so is only used
+  * in cases where the zig version is specified through WITHOUT the use of a plus
+  * sign. It needs to fetch data from the index files provided by zig (or mach)
+  * to determine the appropriate downloadUrl, etc.
+  *
+  * @returns {string} download URL for the version
+  * @returns {string} variant name for the version - should be used as cache key
+  * @returns {string} version name - use for display only
+  */
 async function resolveVersion (arch, platform, version) {
   const ext = extForPlatform(platform)
   const resolvedOs = {
@@ -69,20 +90,29 @@ async function resolveVersion (arch, platform, version) {
 
   const host = `${resolvedArch}-${resolvedOs}`
 
-  const index = await getJSON({ url: 'https://ziglang.org/download/index.json' })
+  // const index = await getJSON({ url: 'https://ziglang.org/download/index.json' })
+  const machIndex = await getJSON({ url: 'https://machengine.org/zig/index.json' })
 
-  const availableVersions = Object.keys(index)
+  const availableVersions = Object.keys(machIndex)
   const useVersion = semver.valid(version)
     ? semver.maxSatisfying(availableVersions.filter((v) => semver.valid(v)), version)
     : null
 
-  const meta = index[useVersion || version]
+  // The mach index is advertised as a strict superset of the ziglang index,
+  // but we will fall back to the the ziglang index just in case
+  const meta = machIndex[useVersion || version] ||
+    (await getJSON({ url: 'https://ziglang.org/download/index.json' }))[useVersion || version]
+
   if (!meta || !meta[host]) {
     throw new Error(`Could not find version ${useVersion || version} for platform ${host}`)
   }
 
   const downloadUrl = meta[host].tarball
-  const variantName = path.basename(meta[host].tarball).replace(`.${ext}`, '')
+  // If this is mach, we could end up with '+sha...' at the end of this, as
+  // a version of '2024.1.0-mach' will resolve to a specific dev version
+  // So, while the function is not called with "+...", we still have to deal with
+  // it. This is important as it is used as the cache key
+  const variantName = path.basename(meta[host].tarball).replace(`.${ext}`, '').replace(/\+\S*$/, '')
 
   return { downloadUrl, variantName, version: useVersion || version }
 }