diff --git a/README.md b/README.md
index a653acb..6669cd7 100644
--- a/README.md
+++ b/README.md
@@ -42,5 +42,6 @@ Be aware of S3 transfer costs if your runners are not in the same AWS region as
 ## Special environment variables
 
 * `RUNS_ON_S3_BUCKET_CACHE`: if set, the action will use this bucket to store the cache.
+* `RUNS_ON_RUNNER_NAME`: if set to `""` and running from RunsOn, the action will not ignore AWS credentials from the environment, if any.
 * `RUNS_ON_S3_FORCE_PATH_STYLE` or `AWS_S3_FORCE_PATH_STYLE`: if one of those environment variables equals the string `"true"`, then the S3 client will be configured to force the path style.
 
diff --git a/src/custom/backend.ts b/src/custom/backend.ts
index 28edba2..cb01941 100644
--- a/src/custom/backend.ts
+++ b/src/custom/backend.ts
@@ -26,7 +26,7 @@ export interface ArtifactCacheEntry {
 
 // if executing from RunsOn, unset any existing AWS env variables so that we can use the IAM instance profile for credentials
 // see unsetCredentials() in https://github.com/aws-actions/configure-aws-credentials/blob/v4.0.2/src/helpers.ts#L44
-if (process.env.RUNS_ON_RUNNER_NAME) {
+if (process.env.RUNS_ON_RUNNER_NAME && process.env.RUNS_ON_RUNNER_NAME !== "") {
     delete process.env.AWS_ACCESS_KEY_ID;
     delete process.env.AWS_SECRET_ACCESS_KEY;
     delete process.env.AWS_SESSION_TOKEN;