diff --git a/bootstrapvz/providers/ec2/__init__.py b/bootstrapvz/providers/ec2/__init__.py
index 4d3a562..b77dfdb 100644
--- a/bootstrapvz/providers/ec2/__init__.py
+++ b/bootstrapvz/providers/ec2/__init__.py
@@ -39,17 +39,24 @@ def validate_manifest(data, validator, error):
 
 	bootloader = data['system']['bootloader']
 	virtualization = data['virtualization']
+	backing = data['volume']['backing']
 	partition_type = data['volume']['partitions']['type']
 
 	if virtualization == 'pvm' and bootloader != 'pvgrub':
 		error('Paravirtualized AMIs only support pvgrub as a bootloader', ['system', 'bootloader'])
 
 	if virtualization == 'hvm':
+		if backing != 'ebs':
+			error('HVM AMIs currently only work when they are EBS backed', ['volume', 'backing'])
 		if bootloader != 'extlinux':
-			error('HVM AMIs only support extlinux as a bootloader', ['system', 'bootloader'])
+			error('HVM AMIs currently only work with extlinux as a bootloader', ['system', 'bootloader'])
 		if bootloader == 'extlinux' and partition_type not in ['none', 'msdos']:
-			error('HVM AMIs booted with extlinux currently only support the `none\' or `msdos\' partition type',
-			      ['system', 'bootloader'])
+			error('HVM AMIs booted with extlinux currently work with unpartitioned or msdos partitions volumes',
+			      ['volume', 'partitions', 'type'])
+
+	if backing == 's3':
+		if partition_type != 'none':
+			error('S3 backed AMIs currently only work with unpartitioned volumes', ['system', 'bootloader'])
 
 
 def resolve_tasks(taskset, manifest):
diff --git a/bootstrapvz/providers/ec2/manifest-schema-s3.json b/bootstrapvz/providers/ec2/manifest-schema-s3.json
index c8012a3..ef23e51 100644
--- a/bootstrapvz/providers/ec2/manifest-schema-s3.json
+++ b/bootstrapvz/providers/ec2/manifest-schema-s3.json
@@ -28,17 +28,6 @@
 				}
 			},
 			"required": ["bucket", "region"]
-		},
-		"volume": {
-			"type": "object",
-			"properties": {
-				"partitions": {
-					"type": "object",
-					"properties": {
-						"type": { "enum": ["none"] }
-					}
-				}
-			}
 		}
 	},
 	"required": ["image"],
diff --git a/bootstrapvz/providers/ec2/manifest-schema.json b/bootstrapvz/providers/ec2/manifest-schema.json
index 3bcc40d..bb4bd97 100644
--- a/bootstrapvz/providers/ec2/manifest-schema.json
+++ b/bootstrapvz/providers/ec2/manifest-schema.json
@@ -39,7 +39,7 @@
 				"partitions": {
 					"type": "object",
 					"properties": {
-						"type": { "enum": ["none", "msdos"] }
+						"type": { "enum": ["none", "msdos", "gpt"] }
 					}
 				}
 			},