diff --git a/repo2docker/app.py b/repo2docker/app.py
index 7820f0b4..562fa1cf 100644
--- a/repo2docker/app.py
+++ b/repo2docker/app.py
@@ -176,9 +176,9 @@ class Repo2Docker(Application):
             sys.exit(1)
 
         if ref:
-            if len(ref.split('/')) != 2:
-                raise ValueError('Expected --ref to be of the form '
-                                 'remote/reference, but got %s' % ref)
+            if self.repo_type == "remote" and len(ref.split('/')) < 2:
+                # Ensure that the ref has `origin` in front
+                ref = '/'.join(["origin", ref])
             try:
                 for line in execute_cmd(['git', 'reset', '--hard', ref],
                                         cwd=checkout_path,
@@ -248,8 +248,8 @@ class Repo2Docker(Application):
 
         argparser.add_argument(
             '--ref',
-            help=('If building a git url, which reference to check out. Must '
-                  'be of the form `remote/reference`. E.g., `origin/master`.')
+            help=('If building a git url, which reference to check out. '
+                  'E.g., `master`.')
         )
 
         argparser.add_argument(
diff --git a/tests/argumentvalidation.py b/tests/argumentvalidation.py
index e1a73e9c..f38c056c 100644
--- a/tests/argumentvalidation.py
+++ b/tests/argumentvalidation.py
@@ -230,13 +230,3 @@ def test_docker_no_build_success():
     builddir = os.path.dirname(__file__) + '/../'
 
     assert validate_arguments(builddir, args_list, "", True)
-
-
-def test_ref_has_correct_form():
-    """
-    Test to check if --ref is given with the form `remote/reference`
-    """
-    builddir = os.path.dirname(__file__)
-    args_list = ['--no-run', '--no-build', '--ref', 'myreference']
-
-    assert not validate_arguments(builddir, args_list, 'Expected --ref to be of the form remote/reference, but got myreference')
diff --git a/tests/external/reproductions.repos.yaml b/tests/external/reproductions.repos.yaml
index e69b6068..defba917 100644
--- a/tests/external/reproductions.repos.yaml
+++ b/tests/external/reproductions.repos.yaml
@@ -3,3 +3,8 @@
   url: https://github.com/minrk/ligo-binder/
   ref: origin/b8259dac9eb
   verify: python -c 'import matplotlib'
+# To test that ref is added if not present
+- name: LIGO Gravitational Waves
+  url: https://github.com/minrk/ligo-binder/
+  ref: b8259dac9eb
+  verify: python -c 'import matplotlib'