diff --git a/compose/config/config.py b/compose/config/config.py
index 4fddac822..2a81b93da 100644
--- a/compose/config/config.py
+++ b/compose/config/config.py
@@ -24,6 +24,7 @@ from .environment import split_env
 from .errors import CircularReference
 from .errors import ComposeFileNotFound
 from .errors import ConfigurationError
+from .errors import DuplicateOverrideFileFound
 from .errors import VERSION_EXPLANATION
 from .interpolation import interpolate_environment_variables
 from .sort_services import get_container_name_from_network_mode
@@ -128,7 +129,7 @@ SUPPORTED_FILENAMES = [
     'docker-compose.yaml',
 ]
 
-DEFAULT_OVERRIDE_FILENAME = 'docker-compose.override.yml'
+DEFAULT_OVERRIDE_FILENAMES = ('docker-compose.override.yml', 'docker-compose.override.yaml')
 
 
 log = logging.getLogger(__name__)
@@ -292,8 +293,12 @@ def get_default_config_files(base_dir):
 
 
 def get_default_override_file(path):
-    override_filename = os.path.join(path, DEFAULT_OVERRIDE_FILENAME)
-    return [override_filename] if os.path.exists(override_filename) else []
+    override_files_in_path = [os.path.join(path, override_filename) for override_filename
+                              in DEFAULT_OVERRIDE_FILENAMES
+                              if os.path.exists(os.path.join(path, override_filename))]
+    if len(override_files_in_path) > 1:
+        raise DuplicateOverrideFileFound(override_files_in_path)
+    return override_files_in_path
 
 
 def find_candidates_in_parent_dirs(filenames, path):
diff --git a/compose/config/errors.py b/compose/config/errors.py
index 9b82df0ab..ac1d3ac19 100644
--- a/compose/config/errors.py
+++ b/compose/config/errors.py
@@ -44,3 +44,12 @@ class ComposeFileNotFound(ConfigurationError):
 
         Supported filenames: %s
         """ % ", ".join(supported_filenames))
+
+
+class DuplicateOverrideFileFound(ConfigurationError):
+    def __init__(self, override_filenames):
+        self.override_filenames = override_filenames
+        super(DuplicateOverrideFileFound, self).__init__(
+            "Multiple override files found: {}. You may only use a single "
+            "override file.".format(", ".join(override_filenames))
+        )
diff --git a/tests/acceptance/cli_test.py b/tests/acceptance/cli_test.py
index 30eff1b6a..1ba64201f 100644
--- a/tests/acceptance/cli_test.py
+++ b/tests/acceptance/cli_test.py
@@ -21,6 +21,7 @@ from docker import errors
 from .. import mock
 from ..helpers import create_host_file
 from compose.cli.command import get_project
+from compose.config.errors import DuplicateOverrideFileFound
 from compose.container import Container
 from compose.project import OneOffFilter
 from compose.utils import nanoseconds_from_time_seconds
@@ -31,7 +32,6 @@ from tests.integration.testcases import v2_1_only
 from tests.integration.testcases import v2_only
 from tests.integration.testcases import v3_only
 
-
 ProcessResult = namedtuple('ProcessResult', 'stdout stderr')
 
 
@@ -2149,3 +2149,25 @@ class CLITestCase(DockerClientTestCase):
         assert 'busybox' in result.stdout
         assert 'multiplecomposefiles_another_1' in result.stdout
         assert 'multiplecomposefiles_simple_1' in result.stdout
+
+    def test_up_with_override_yaml(self):
+        self.base_dir = 'tests/fixtures/override-yaml-files'
+        self._project = get_project(self.base_dir, [])
+        self.dispatch(
+            [
+                'up', '-d',
+            ],
+            None)
+
+        containers = self.project.containers()
+        self.assertEqual(len(containers), 2)
+
+        web, db = containers
+        self.assertEqual(web.human_readable_command, 'sleep 100')
+        self.assertEqual(db.human_readable_command, 'top')
+
+    def test_up_with_duplicate_override_yaml_files(self):
+        self.base_dir = 'tests/fixtures/duplicate-override-yaml-files'
+        with self.assertRaises(DuplicateOverrideFileFound):
+            get_project(self.base_dir, [])
+        self.base_dir = None
diff --git a/tests/fixtures/duplicate-override-yaml-files/docker-compose.override.yaml b/tests/fixtures/duplicate-override-yaml-files/docker-compose.override.yaml
new file mode 100644
index 000000000..58c673482
--- /dev/null
+++ b/tests/fixtures/duplicate-override-yaml-files/docker-compose.override.yaml
@@ -0,0 +1,3 @@
+
+db:
+    command: "top"
diff --git a/tests/fixtures/duplicate-override-yaml-files/docker-compose.override.yml b/tests/fixtures/duplicate-override-yaml-files/docker-compose.override.yml
new file mode 100644
index 000000000..f1b8ef181
--- /dev/null
+++ b/tests/fixtures/duplicate-override-yaml-files/docker-compose.override.yml
@@ -0,0 +1,3 @@
+
+db:
+    command: "sleep 300"
diff --git a/tests/fixtures/duplicate-override-yaml-files/docker-compose.yml b/tests/fixtures/duplicate-override-yaml-files/docker-compose.yml
new file mode 100644
index 000000000..5f2909d69
--- /dev/null
+++ b/tests/fixtures/duplicate-override-yaml-files/docker-compose.yml
@@ -0,0 +1,10 @@
+
+web:
+    image: busybox:latest
+    command: "sleep 100"
+    links:
+        - db
+
+db:
+    image: busybox:latest
+    command: "sleep 200"
diff --git a/tests/fixtures/override-yaml-files/docker-compose.override.yaml b/tests/fixtures/override-yaml-files/docker-compose.override.yaml
new file mode 100644
index 000000000..58c673482
--- /dev/null
+++ b/tests/fixtures/override-yaml-files/docker-compose.override.yaml
@@ -0,0 +1,3 @@
+
+db:
+    command: "top"
diff --git a/tests/fixtures/override-yaml-files/docker-compose.yml b/tests/fixtures/override-yaml-files/docker-compose.yml
new file mode 100644
index 000000000..5f2909d69
--- /dev/null
+++ b/tests/fixtures/override-yaml-files/docker-compose.yml
@@ -0,0 +1,10 @@
+
+web:
+    image: busybox:latest
+    command: "sleep 100"
+    links:
+        - db
+
+db:
+    image: busybox:latest
+    command: "sleep 200"