diff --git a/compose/config/fields_schema.json b/compose/config/fields_schema.json
index 7723f2fbc..a174ba873 100644
--- a/compose/config/fields_schema.json
+++ b/compose/config/fields_schema.json
@@ -2,15 +2,18 @@
   "$schema": "http://json-schema.org/draft-04/schema#",
 
   "type": "object",
+  "id": "fields_schema.json",
 
   "patternProperties": {
     "^[a-zA-Z0-9._-]+$": {
       "$ref": "#/definitions/service"
     }
   },
+  "additionalProperties": false,
 
   "definitions": {
     "service": {
+      "id": "#/definitions/service",
       "type": "object",
 
       "properties": {
@@ -167,6 +170,5 @@
       ]
     }
 
-  },
-  "additionalProperties": false
+  }
 }
diff --git a/compose/config/service_schema.json b/compose/config/service_schema.json
index 221c5d8d7..05774efdd 100644
--- a/compose/config/service_schema.json
+++ b/compose/config/service_schema.json
@@ -1,15 +1,17 @@
 {
   "$schema": "http://json-schema.org/draft-04/schema#",
+  "id": "service_schema.json",
 
   "type": "object",
 
   "allOf": [
     {"$ref": "fields_schema.json#/definitions/service"},
-    {"$ref": "#/definitions/service_constraints"}
+    {"$ref": "#/definitions/constraints"}
   ],
 
   "definitions": {
-    "service_constraints": {
+    "constraints": {
+      "id": "#/definitions/constraints",
       "anyOf": [
         {
           "required": ["build"],
@@ -21,13 +23,8 @@
             {"required": ["build"]},
             {"required": ["dockerfile"]}
           ]}
-        },
-        {
-          "required": ["extends"],
-          "not": {"required": ["build", "image"]}
         }
       ]
     }
   }
-
 }
diff --git a/compose/config/validation.py b/compose/config/validation.py
index d3bcb35c4..962d41e2f 100644
--- a/compose/config/validation.py
+++ b/compose/config/validation.py
@@ -307,7 +307,10 @@ def _validate_against_schema(config, schema_filename, format_checker=[], service
         schema = json.load(schema_fh)
 
     resolver = RefResolver(resolver_full_path, schema)
-    validation_output = Draft4Validator(schema, resolver=resolver, format_checker=FormatChecker(format_checker))
+    validation_output = Draft4Validator(
+        schema,
+        resolver=resolver,
+        format_checker=FormatChecker(format_checker))
 
     errors = [error for error in sorted(validation_output.iter_errors(config), key=str)]
     if errors:
diff --git a/tests/unit/config/config_test.py b/tests/unit/config/config_test.py
index add7a5a48..03e338cbb 100644
--- a/tests/unit/config/config_test.py
+++ b/tests/unit/config/config_test.py
@@ -78,14 +78,12 @@ class ConfigTest(unittest.TestCase):
 
     def test_config_invalid_service_names(self):
         for invalid_name in ['?not?allowed', ' ', '', '!', '/', '\xe2']:
-            with pytest.raises(ConfigurationError):
-                config.load(
-                    build_config_details(
-                        {invalid_name: {'image': 'busybox'}},
-                        'working_dir',
-                        'filename.yml'
-                    )
-                )
+            with pytest.raises(ConfigurationError) as exc:
+                config.load(build_config_details(
+                    {invalid_name: {'image': 'busybox'}},
+                    'working_dir',
+                    'filename.yml'))
+            assert 'Invalid service name \'%s\'' % invalid_name in exc.exconly()
 
     def test_load_with_invalid_field_name(self):
         config_details = build_config_details(
@@ -97,6 +95,16 @@ class ConfigTest(unittest.TestCase):
         error_msg = "Unsupported config option for 'web' service: 'name'"
         assert error_msg in exc.exconly()
 
+    def test_load_invalid_service_definition(self):
+        config_details = build_config_details(
+            {'web': 'wrong'},
+            'working_dir',
+            'filename.yml')
+        with pytest.raises(ConfigurationError) as exc:
+            config.load(config_details)
+        error_msg = "Service \"web\" doesn\'t have any configuration options"
+        assert error_msg in exc.exconly()
+
     def test_config_integer_service_name_raise_validation_error(self):
         expected_error_msg = "Service name: 1 needs to be a string, eg '1'"
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
diff --git a/tox.ini b/tox.ini
index f05c5ed26..d1098a55a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -43,4 +43,6 @@ directory = coverage-html
 [flake8]
 # Allow really long lines for now
 max-line-length = 140
+# Set this high for now
+max-complexity = 20
 exclude = compose/packages