diff --git a/README.md b/README.md
index 5aeed8a..fe62dff 100644
--- a/README.md
+++ b/README.md
@@ -34,6 +34,13 @@ Optionally set a Zig version:
     version: 0.4.0 # The default is 0.5.0
 ```
 
+To use the nightly builds, set:
+```yaml
+- uses: goto-bus-stop/setup-zig@v1.0.0
+  with:
+    version: master
+```
+
 If you are running Zig on Windows machines, you need to make sure that your .zig files use \n line endings and not \r\n. The `actions/checkout` action auto-converts line endings to \r\n, so add a `.gitattributes` file:
 ```
 *.zig text eol=lf
diff --git a/index.js b/index.js
index e0753f8..cdc13be 100644
--- a/index.js
+++ b/index.js
@@ -31,8 +31,10 @@ async function downloadZig (version) {
 
   const index = await getJSON({ url: 'https://ziglang.org/download/index.json' })
 
-  const availableVersions = Object.keys(index).filter((v) => semver.valid(v))
-  const useVersion = semver.maxSatisfying(availableVersions, version)
+  const availableVersions = Object.keys(index)
+  const useVersion = semver.valid(version)
+    ? semver.maxSatisfying(availableVersions.filter((v) => semver.valid(v)), version)
+    : null
 
   const meta = index[useVersion || version]
   if (!meta || !meta[host]) {
@@ -56,7 +58,7 @@ async function downloadZig (version) {
 
 async function main () {
   const version = actions.getInput('version') || '0.5.0'
-  if (semver.lt(version, '0.3.0')) {
+  if (semver.valid(version) && semver.lt(version, '0.3.0')) {
     actions.setFailed('This action does not work with Zig 0.1.0 and Zig 0.2.0')
     return
   }