diff --git a/src/config.ts b/src/config.ts
index 53f5b5f6..188ada70 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -60,7 +60,7 @@ export function makeConfig() {
       ] as const,
     }),
     stackName: getInput('stack-name', { required: true }),
-    pulumiVersion: getInput('pulumi-version') ?? '^3',
+    pulumiVersion: getInput('pulumi-version', { required: true }),
     workDir: getInput('work-dir', { required: true }),
     secretsProvider: getInput('secrets-provider'),
     cloudUrl: getInput('cloud-url'),