diff --git a/src/storage/s3.js b/src/storage/s3.js
index ab45abafe..6cb5ff032 100644
--- a/src/storage/s3.js
+++ b/src/storage/s3.js
@@ -155,6 +155,7 @@ function exists(apiConfig, backupFilePath, callback) {
             };
 
             s3.headObject(params, function (error) {
+                if (!Object.keys(this.httpResponse.headers).some(h => h.startsWith('x-amz'))) return callback(new BoxError(BoxError.EXTERNAL_ERROR, 'not a s3 endpoint'));
                 if (error && S3_NOT_FOUND(error)) return callback(null, false);
                 if (error) return callback(new BoxError(BoxError.EXTERNAL_ERROR, error.message || error.code));