diff --git a/plugins/image_commands/__init__.py b/plugins/image_commands/__init__.py
index 5353b48..8a9f189 100644
--- a/plugins/image_commands/__init__.py
+++ b/plugins/image_commands/__init__.py
@@ -1,11 +1,11 @@
 
 
+def validate_manifest(data, schema_validate):
+	from os import path
+	schema_path = path.normpath(path.join(path.dirname(__file__), 'manifest-schema.json'))
+	schema_validate(data, schema_path)
+
+
 def tasks(tasklist, manifest):
-        from image_commands import ImageExecuteCommand
-        tasklist.add(ImageExecuteCommand())
-
-def validate_manifest(data, schema_validate):
-        from os import path
-        schema_path = path.normpath(path.join(path.dirname(__file__), 'manifest-schema.json'))
-        schema_validate(data, schema_path)
-
+	from image_commands import ImageExecuteCommand
+	tasklist.add(ImageExecuteCommand)
diff --git a/plugins/image_commands/image_commands.py b/plugins/image_commands/image_commands.py
index f79f835..71781aa 100644
--- a/plugins/image_commands/image_commands.py
+++ b/plugins/image_commands/image_commands.py
@@ -3,20 +3,17 @@ from common import phases
 
 
 class ImageExecuteCommand(Task):
-    description = 'Execute command in the image'
-    phase = phases.system_modification
-
-    def run(self, info):
-        from common.tools import log_check_call
-
-        for user_cmd in info.manifest.plugins['image_commands']['commands']:
-            command = []
-            for elt in user_cmd:
-                fragment = elt.format(
-                                root=info.root,
-                                image=info.loopback_file,
-                                filesystem=info.manifest.volume['filesystem'])
-                command.append(fragment) 
-            log_check_call(command)
+	description = 'Execute command in the image'
+	phase = phases.system_modification
 
+	def run(self, info):
+		from common.tools import log_check_call
 
+		for user_cmd in info.manifest.plugins['image_commands']['commands']:
+			command = []
+			for elt in user_cmd:
+				fragment = elt.format(root=info.root,
+				                      image=info.loopback_file,
+				                      filesystem=info.manifest.volume['filesystem'])
+				command.append(fragment)
+			log_check_call(command)
diff --git a/plugins/image_commands/manifest-schema.json b/plugins/image_commands/manifest-schema.json
index f57b2e8..9785c90 100644
--- a/plugins/image_commands/manifest-schema.json
+++ b/plugins/image_commands/manifest-schema.json
@@ -13,10 +13,10 @@
 							"type": "array",
 							"items": {
 								"type": "array",
-								"items": {
-									"type": "string"
-									}
-							}
+								"items": {"type": "string"},
+								"minItems": 1
+							},
+							"minItems": 1
 						}
 					},
 					"required": ["commands"]
diff --git a/plugins/user_packages/__init__.py b/plugins/user_packages/__init__.py
index 218975c..3596486 100644
--- a/plugins/user_packages/__init__.py
+++ b/plugins/user_packages/__init__.py
@@ -1,6 +1,14 @@
 
 
+def validate_manifest(data, schema_validate):
+	from os import path
+	schema_path = path.normpath(path.join(path.dirname(__file__), 'manifest-schema.json'))
+	schema_validate(data, schema_path)
+
+
 def tasks(tasklist, manifest):
 	from user_packages import AddUserPackages, AddLocalUserPackages
-	tasklist.add(AddUserPackages,
-	             AddLocalUserPackages)
+	if 'repo' in manifest.plugins['user_packages']:
+		tasklist.add(AddUserPackages)
+	if 'local' in manifest.plugins['user_packages']:
+		tasklist.add(AddLocalUserPackages)
diff --git a/plugins/user_packages/manifest-schema.json b/plugins/user_packages/manifest-schema.json
new file mode 100644
index 0000000..865701c
--- /dev/null
+++ b/plugins/user_packages/manifest-schema.json
@@ -0,0 +1,33 @@
+{
+	"$schema": "http://json-schema.org/draft-04/schema#",
+	"title": "Image commands plugin manifest",
+	"type": "object",
+	"properties": {
+		"plugins": {
+			"type": "object",
+			"properties": {
+				"user_packages": {
+					"type": "object",
+					"properties": {
+						"repo": {
+							"type": "array",
+							"items": {"type": "string"},
+							"minItems": 1
+						},
+						"local": {
+							"type": "array",
+							"items": {"type": "string"},
+							"minItems": 1
+						}
+					},
+					"anyOf": [
+						{"required": ["repo"]},
+						{"required": ["local"]}
+          ]
+				}
+			},
+			"required": ["user_packages"]
+		}
+	},
+	"required": ["plugins"]
+}
diff --git a/plugins/user_packages/user_packages.py b/plugins/user_packages/user_packages.py
index 7739358..6ab39a8 100644
--- a/plugins/user_packages/user_packages.py
+++ b/plugins/user_packages/user_packages.py
@@ -13,8 +13,6 @@ class AddUserPackages(Task):
 	successors = [CheckPackages]
 
 	def run(self, info):
-		if 'repo' not in info.manifest.plugins['user_packages']:
-			return
 		for pkg in info.manifest.plugins['user_packages']['repo']:
 			info.img_packages[0].add(pkg)
 
@@ -25,9 +23,6 @@ class AddLocalUserPackages(Task):
 	predecessors = [MountRoot]
 
 	def run(self, info):
-		if 'local' not in info.manifest.plugins['user_packages']:
-			return
-
 		import stat
 		rwxr_xr_x = (stat.S_IRUSR | stat.S_IWUSR | stat.S_IXUSR |
 		             stat.S_IRGRP                | stat.S_IXGRP |