diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 36354f7b4..a32251621 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -17,7 +17,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-20.04, ubuntu-22.04, ubuntu-24.04, macos-12, macos-13, macos-14, windows-2019, windows-2022 ]
+        os: [ ubuntu-20.04, ubuntu-22.04, ubuntu-24.04, macos-12, macos-13, macos-14, macos-15, windows-2019, windows-2022 ]
         ruby: [
           '1.9', '2.0', '2.1', '2.2', '2.3', '2.4', '2.5', '2.6', '2.7', '3.0', '3.1', '3.2', '3.3', ruby-head,
           jruby, jruby-head,
@@ -35,7 +35,7 @@ jobs:
         - { os: ubuntu-22.04, ruby: '2.2' }
         - { os: ubuntu-24.04, ruby: '1.9' }
         - { os: ubuntu-24.04, ruby: '2.2' }
-        # These old Rubies fail to compile on macos-14 (macOS 14, arm64), which is used for ruby/ruby-builder
+        # These old Rubies fail to compile on macOS arm64
         - { os: macos-14, ruby: '1.9' }
         - { os: macos-14, ruby: '2.0' }
         - { os: macos-14, ruby: '2.1' }
@@ -43,6 +43,13 @@ jobs:
         - { os: macos-14, ruby: '2.3' }
         - { os: macos-14, ruby: '2.4' }
         - { os: macos-14, ruby: '2.5' }
+        - { os: macos-15, ruby: '1.9' }
+        - { os: macos-15, ruby: '2.0' }
+        - { os: macos-15, ruby: '2.1' }
+        - { os: macos-15, ruby: '2.2' }
+        - { os: macos-15, ruby: '2.3' }
+        - { os: macos-15, ruby: '2.4' }
+        - { os: macos-15, ruby: '2.5' }
         # Windows
         - { os: windows-2019, ruby: '1.9' }
         - { os: windows-2019, ruby: debug }
diff --git a/common.js b/common.js
index 61d0021d1..cd4dd2766 100644
--- a/common.js
+++ b/common.js
@@ -162,73 +162,103 @@ export async function hashFile(file) {
   return hash.digest('hex')
 }
 
+// macos is not listed explicitly, see below
 const GitHubHostedPlatforms = [
   'ubuntu-20.04-x64',
   'ubuntu-22.04-x64',
   'ubuntu-24.04-x64',
-  'macos-12-x64',
-  'macos-13-x64',
-  'macos-13-arm64',
-  'macos-14-x64',
-  'macos-14-arm64',
   'windows-2019-x64',
   'windows-2022-x64',
 ]
 
+// Precisely: whether we have builds for that platform and there are GitHub-hosted runners to test it
+function isSupportedPlatform() {
+  const platform = getOSName()
+  switch (platform) {
+    case 'ubuntu':
+      return GitHubHostedPlatforms.includes(getOSNameVersionArch())
+    case 'macos':
+      // See https://github.com/ruby/ruby-builder/blob/master/README.md#naming
+      // 13 on arm64 because of old macos-arm-oss runners
+      return (os.arch() === 'x64' && parseInt(getOSVersion()) >= 12) ||
+          (os.arch() === 'arm64' && parseInt(getOSVersion()) >= 13)
+    case 'windows':
+      return GitHubHostedPlatforms.includes(getOSNameVersionArch())
+  }
+}
+
 // Actually a self-hosted runner for which the OS and OS version does not correspond to a GitHub-hosted runner image,
 export function isSelfHostedRunner() {
   if (inputs.selfHosted === undefined) {
     throw new Error('inputs.selfHosted should have been already set')
   }
 
-  return inputs.selfHosted === 'true' ||
-    !GitHubHostedPlatforms.includes(getOSNameVersionArch())
+  return inputs.selfHosted === 'true' || !isSupportedPlatform()
 }
 
 export function selfHostedRunnerReason() {
   if (inputs.selfHosted === 'true') {
     return 'the self-hosted input was set'
-  } else if (!GitHubHostedPlatforms.includes(getOSNameVersionArch())) {
+  } else if (!isSupportedPlatform()) {
     return 'the platform does not match a GitHub-hosted runner image (or that image is deprecated and no longer supported)'
   } else {
     return 'unknown reason'
   }
 }
 
-let osNameVersion = undefined
+let osName = undefined
+let osVersion = undefined
 
-export function getOSNameVersion() {
-  if (osNameVersion !== undefined) {
-    return osNameVersion
+export function getOSName() {
+  if (osName !== undefined) {
+    return osName
   }
 
   const platform = os.platform()
-  let osName
-  let osVersion
   if (platform === 'linux') {
     const info = linuxOSInfo({mode: 'sync'})
     osName = info.id
-    osVersion = info.version_id
   } else if (platform === 'darwin') {
     osName = 'macos'
-    osVersion = macosRelease().version
   } else if (platform === 'win32') {
     osName = 'windows'
+  } else {
+    throw new Error(`Unknown platform ${platform}`)
+  }
+
+  return osName
+}
+
+export function getOSVersion() {
+  if (osVersion !== undefined) {
+    return osVersion
+  }
+
+  const platform = os.platform()
+  if (platform === 'linux') {
+    const info = linuxOSInfo({mode: 'sync'})
+    osVersion = info.version_id
+  } else if (platform === 'darwin') {
+    osVersion = macosRelease().version
+  } else if (platform === 'win32') {
     osVersion = findWindowsVersion()
   } else {
     throw new Error(`Unknown platform ${platform}`)
   }
 
-  osNameVersion = `${osName}-${osVersion}`
-  return osNameVersion
+  return osVersion
+}
+
+export function getOSNameVersion() {
+  return `${getOSName()}-${getOSVersion()}`
 }
 
 export function getOSNameVersionArch() {
-  return `${getOSNameVersion()}-${os.arch()}`
+  return `${getOSName()}-${getOSVersion()}-${os.arch()}`
 }
 
 function findWindowsVersion() {
-  const version = os.version();
+  const version = os.version()
   const match = version.match(/^Windows Server (\d+) Datacenter/)
   if (match) {
     return match[1]
@@ -261,15 +291,14 @@ export function getRunnerToolCache() {
 
 // Rubies prebuilt by this action embed this path rather than using $RUNNER_TOOL_CACHE
 function getDefaultToolCachePath() {
-  const platform = getOSNameVersion()
-  if (platform.startsWith('ubuntu-')) {
-    return '/opt/hostedtoolcache'
-  } else if (platform.startsWith('macos-')) {
-    return '/Users/runner/hostedtoolcache'
-  } else if (platform.startsWith('windows-')) {
-    return 'C:\\hostedtoolcache\\windows'
-  } else {
-    throw new Error('Unknown platform')
+  const platform = getOSName()
+  switch (platform) {
+    case 'ubuntu':
+      return '/opt/hostedtoolcache'
+    case 'macos':
+      return '/Users/runner/hostedtoolcache'
+    case 'windows':
+      return 'C:\\hostedtoolcache\\windows'
   }
 }
 
diff --git a/dist/index.js b/dist/index.js
index 61c20642e..c7c936f22 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -292,8 +292,10 @@ __nccwpck_require__.d(__webpack_exports__, {
   "createToolCacheCompleteFile": () => (/* binding */ createToolCacheCompleteFile),
   "drive": () => (/* binding */ drive),
   "floatVersion": () => (/* binding */ floatVersion),
+  "getOSName": () => (/* binding */ getOSName),
   "getOSNameVersion": () => (/* binding */ getOSNameVersion),
   "getOSNameVersionArch": () => (/* binding */ getOSNameVersionArch),
+  "getOSVersion": () => (/* binding */ getOSVersion),
   "getRunnerToolCache": () => (/* binding */ getRunnerToolCache),
   "getToolCachePath": () => (/* binding */ getToolCachePath),
   "getToolCacheRubyPrefix": () => (/* binding */ getToolCacheRubyPrefix),
@@ -523,73 +525,103 @@ async function hashFile(file) {
   return hash.digest('hex')
 }
 
+// macos is not listed explicitly, see below
 const GitHubHostedPlatforms = [
   'ubuntu-20.04-x64',
   'ubuntu-22.04-x64',
   'ubuntu-24.04-x64',
-  'macos-12-x64',
-  'macos-13-x64',
-  'macos-13-arm64',
-  'macos-14-x64',
-  'macos-14-arm64',
   'windows-2019-x64',
   'windows-2022-x64',
 ]
 
+// Precisely: whether we have builds for that platform and there are GitHub-hosted runners to test it
+function isSupportedPlatform() {
+  const platform = getOSName()
+  switch (platform) {
+    case 'ubuntu':
+      return GitHubHostedPlatforms.includes(getOSNameVersionArch())
+    case 'macos':
+      // See https://github.com/ruby/ruby-builder/blob/master/README.md#naming
+      // 13 on arm64 because of old macos-arm-oss runners
+      return (os.arch() === 'x64' && parseInt(getOSVersion()) >= 12) ||
+          (os.arch() === 'arm64' && parseInt(getOSVersion()) >= 13)
+    case 'windows':
+      return GitHubHostedPlatforms.includes(getOSNameVersionArch())
+  }
+}
+
 // Actually a self-hosted runner for which the OS and OS version does not correspond to a GitHub-hosted runner image,
 function isSelfHostedRunner() {
   if (inputs.selfHosted === undefined) {
     throw new Error('inputs.selfHosted should have been already set')
   }
 
-  return inputs.selfHosted === 'true' ||
-    !GitHubHostedPlatforms.includes(getOSNameVersionArch())
+  return inputs.selfHosted === 'true' || !isSupportedPlatform()
 }
 
 function selfHostedRunnerReason() {
   if (inputs.selfHosted === 'true') {
     return 'the self-hosted input was set'
-  } else if (!GitHubHostedPlatforms.includes(getOSNameVersionArch())) {
+  } else if (!isSupportedPlatform()) {
     return 'the platform does not match a GitHub-hosted runner image (or that image is deprecated and no longer supported)'
   } else {
     return 'unknown reason'
   }
 }
 
-let osNameVersion = undefined
+let osName = undefined
+let osVersion = undefined
 
-function getOSNameVersion() {
-  if (osNameVersion !== undefined) {
-    return osNameVersion
+function getOSName() {
+  if (osName !== undefined) {
+    return osName
   }
 
   const platform = os.platform()
-  let osName
-  let osVersion
   if (platform === 'linux') {
     const info = linuxOSInfo({mode: 'sync'})
     osName = info.id
-    osVersion = info.version_id
   } else if (platform === 'darwin') {
     osName = 'macos'
-    osVersion = macosRelease().version
   } else if (platform === 'win32') {
     osName = 'windows'
+  } else {
+    throw new Error(`Unknown platform ${platform}`)
+  }
+
+  return osName
+}
+
+function getOSVersion() {
+  if (osVersion !== undefined) {
+    return osVersion
+  }
+
+  const platform = os.platform()
+  if (platform === 'linux') {
+    const info = linuxOSInfo({mode: 'sync'})
+    osVersion = info.version_id
+  } else if (platform === 'darwin') {
+    osVersion = macosRelease().version
+  } else if (platform === 'win32') {
     osVersion = findWindowsVersion()
   } else {
     throw new Error(`Unknown platform ${platform}`)
   }
 
-  osNameVersion = `${osName}-${osVersion}`
-  return osNameVersion
+  return osVersion
+}
+
+function getOSNameVersion() {
+  return `${getOSName()}-${getOSVersion()}`
 }
 
 function getOSNameVersionArch() {
-  return `${getOSNameVersion()}-${os.arch()}`
+  return `${getOSName()}-${getOSVersion()}-${os.arch()}`
 }
 
 function findWindowsVersion() {
-  const version = os.version();
+  const version = os.version()
   const match = version.match(/^Windows Server (\d+) Datacenter/)
   if (match) {
     return match[1]
@@ -622,15 +654,14 @@ function getRunnerToolCache() {
 
 // Rubies prebuilt by this action embed this path rather than using $RUNNER_TOOL_CACHE
 function getDefaultToolCachePath() {
-  const platform = getOSNameVersion()
-  if (platform.startsWith('ubuntu-')) {
-    return '/opt/hostedtoolcache'
-  } else if (platform.startsWith('macos-')) {
-    return '/Users/runner/hostedtoolcache'
-  } else if (platform.startsWith('windows-')) {
-    return 'C:\\hostedtoolcache\\windows'
-  } else {
-    throw new Error('Unknown platform')
+  const platform = getOSName()
+  switch (platform) {
+    case 'ubuntu':
+      return '/opt/hostedtoolcache'
+    case 'macos':
+      return '/Users/runner/hostedtoolcache'
+    case 'windows':
+      return 'C:\\hostedtoolcache\\windows'
   }
 }