diff --git a/compose/config/validation.py b/compose/config/validation.py
index 7347c0128..aa2e0fcf4 100644
--- a/compose/config/validation.py
+++ b/compose/config/validation.py
@@ -99,12 +99,14 @@ def process_errors(errors):
                 if error.validator_value == "array":
                     msg = "an"
 
-                try:
-                    config_key = error.path[1]
-                    type_errors.append("Service '{}' has an invalid value for '{}', it should be {} {}".format(service_name, config_key, msg, error.validator_value))
-                except IndexError:
-                    config_key = error.path[0]
-                    root_msgs.append("Service '{}' doesn\'t have any configuration options. All top level keys in your docker-compose.yml must map to a dictionary of configuration options.'".format(config_key))
+                # pop the service name off our path
+                error.path.popleft()
+
+                if len(error.path) > 0:
+                    config_key = " ".join(["'%s'" % k for k in error.path])
+                    type_errors.append("Service '{}' configuration key {} contains an invalid type, it should be {} {}".format(service_name, config_key, msg, error.validator_value))
+                else:
+                    root_msgs.append("Service '{}' doesn\'t have any configuration options. All top level keys in your docker-compose.yml must map to a dictionary of configuration options.'".format(service_name))
             elif error.validator == 'required':
                 config_key = error.path[1]
                 required.append("Service '{}' option '{}' is invalid, {}".format(service_name, config_key, _clean_error_message(error.message)))
diff --git a/tests/unit/config_test.py b/tests/unit/config_test.py
index e023153a3..0ea375db4 100644
--- a/tests/unit/config_test.py
+++ b/tests/unit/config_test.py
@@ -124,7 +124,7 @@ class ConfigTest(unittest.TestCase):
             )
 
     def test_invalid_config_type_should_be_an_array(self):
-        expected_error_msg = "Service 'foo' has an invalid value for 'links', it should be an array"
+        expected_error_msg = "Service 'foo' configuration key 'links' contains an invalid type, it should be an array"
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
                 config.ConfigDetails(
@@ -690,6 +690,25 @@ class ExtendsTest(unittest.TestCase):
                 )
             )
 
+    def test_extends_validation_sub_property_key(self):
+        expected_error_msg = "Service 'web' configuration key 'extends' 'file' contains an invalid type"
+        with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
+            config.load(
+                config.ConfigDetails(
+                    {
+                        'web': {
+                            'image': 'busybox',
+                            'extends': {
+                                'file': 1,
+                                'service': 'web',
+                            }
+                        },
+                    },
+                    'tests/fixtures/extends',
+                    'filename.yml'
+                )
+            )
+
     def test_extends_validation_no_file_key_no_filename_set(self):
         dictionary = {'extends': {'service': 'web'}}