diff --git a/samcli/commands/package/exceptions.py b/samcli/commands/package/exceptions.py
index fac98490b7..7775949fcd 100644
--- a/samcli/commands/package/exceptions.py
+++ b/samcli/commands/package/exceptions.py
@@ -78,6 +78,15 @@ class NoSuchBucketError(UserException):
     def __init__(self, **kwargs):
         self.kwargs = kwargs
 
-        message_fmt = "\n S3 Bucket does not exist."
+        message_fmt = "\nS3 Bucket does not exist."
 
         super(NoSuchBucketError, self).__init__(message=message_fmt.format(**self.kwargs))
+
+
+class BucketNotSpecifiedError(UserException):
+    def __init__(self, **kwargs):
+        self.kwargs = kwargs
+
+        message_fmt = "\nS3 Bucket not specified, use --s3-bucket to specify a bucket name"
+
+        super(BucketNotSpecifiedError, self).__init__(message=message_fmt.format(**self.kwargs))
diff --git a/samcli/lib/package/s3_uploader.py b/samcli/lib/package/s3_uploader.py
index cf5484e025..d89710c0df 100644
--- a/samcli/lib/package/s3_uploader.py
+++ b/samcli/lib/package/s3_uploader.py
@@ -27,7 +27,7 @@
 
 from boto3.s3 import transfer
 
-from samcli.commands.package.exceptions import NoSuchBucketError
+from samcli.commands.package.exceptions import NoSuchBucketError, BucketNotSpecifiedError
 
 LOG = logging.getLogger(__name__)
 
@@ -134,6 +134,8 @@ def file_exists(self, remote_path):
 
         try:
             # Find the object that matches this ETag
+            if not self.bucket_name:
+                raise BucketNotSpecifiedError()
             self.s3.head_object(Bucket=self.bucket_name, Key=remote_path)
             return True
         except botocore.exceptions.ClientError:
diff --git a/tests/unit/lib/package/test_s3_uploader.py b/tests/unit/lib/package/test_s3_uploader.py
index 40f22f7981..a2aef1e008 100644
--- a/tests/unit/lib/package/test_s3_uploader.py
+++ b/tests/unit/lib/package/test_s3_uploader.py
@@ -7,7 +7,7 @@
 from pathlib import Path
 from botocore.exceptions import ClientError
 
-from samcli.commands.package.exceptions import NoSuchBucketError
+from samcli.commands.package.exceptions import NoSuchBucketError, BucketNotSpecifiedError
 from samcli.lib.package.s3_uploader import S3Uploader
 
 
@@ -144,6 +144,20 @@ def test_s3_upload(self):
             s3_url = s3_uploader.upload(f.name, remote_path)
             self.assertEqual(s3_url, "s3://{0}/{1}/{2}".format(self.bucket_name, self.prefix, remote_path))
 
+    def test_s3_upload_no_bucket(self):
+        s3_uploader = S3Uploader(
+            s3_client=self.s3,
+            bucket_name=None,
+            prefix=self.prefix,
+            kms_key_id=self.kms_key_id,
+            force_upload=self.force_upload,
+        )
+        s3_uploader.artifact_metadata = {"a": "b"}
+        remote_path = Path.joinpath(Path(os.getcwd()), Path("tmp"))
+        with self.assertRaises(BucketNotSpecifiedError):
+            with tempfile.NamedTemporaryFile(mode="w", delete=False) as f:
+                s3_uploader.upload(f.name, remote_path)
+
     def test_s3_upload_with_dedup(self):
         s3_uploader = S3Uploader(
             s3_client=self.s3,