diff --git a/setup.py b/setup.py
index 79c367d..0b3f599 100644
--- a/setup.py
+++ b/setup.py
@@ -16,7 +16,7 @@
 
 setup(
     name="twined",
-    version="0.2.0",
+    version="0.2.1",
     py_modules=[],
     install_requires=["jsonschema ~= 3.2.0", "python-dotenv"],
     url="https://www.github.com/octue/twined",
diff --git a/tests/test_children.py b/tests/test_children.py
index 5f47c2d..0631dbb 100644
--- a/tests/test_children.py
+++ b/tests/test_children.py
@@ -60,8 +60,7 @@ class TestChildrenValidation(BaseTestCase):
                 "id": "some-id",
                 "backend": {
                     "name": "GCPPubSubBackend",
-                    "project_name": "my-project",
-                    "credentials_environment_variable": "GCP_SERVICE_ACCOUNT"
+                    "project_name": "my-project"
                 }
             }
         ]
@@ -72,12 +71,12 @@ def test_no_children(self):
         Twine().validate_children(source=[])
 
     def test_missing_children(self):
-        """Test that a twine with children will not validate on an empty children input"""
+        """Test that a twine with children will not validate on an empty children input."""
         with self.assertRaises(exceptions.InvalidValuesContents):
             Twine(source=self.VALID_TWINE_WITH_CHILDREN).validate_children(source=[])
 
     def test_extra_children(self):
-        """Test that a twine with no children will not validate a non-empty children input"""
+        """Test that a twine with no children will not validate a non-empty children input."""
         with self.assertRaises(exceptions.InvalidValuesContents):
             Twine().validate_children(source=self.VALID_CHILD_VALUE)
 
@@ -111,8 +110,7 @@ def test_extra_key_validation_on_valid_twine(self):
                     "id": "some-id",
                     "backend": {
                         "name": "GCPPubSubBackend",
-                        "project_name": "my-project",
-                        "credentials_environment_variable": "GCP_SERVICE_ACCOUNT"
+                        "project_name": "my-project"
                     },
                     "some_extra_property": "should not be a problem if present"
                 }
diff --git a/twined/schema/children_schema.json b/twined/schema/children_schema.json
index 80b3778..1da053d 100644
--- a/twined/schema/children_schema.json
+++ b/twined/schema/children_schema.json
@@ -27,13 +27,9 @@
                             "project_name": {
                                 "description": "Name of the Google Cloud Platform (GCP) project the child exists in.",
                                 "type": "string"
-                            },
-                            "credentials_environment_variable": {
-                                "description": "Name of environment variable containing either the absolute path to a Google Cloud Platform credentials JSON file or the JSON itself as a string.",
-                                "type": "string"
                             }
                         },
-                        "required": ["name", "project_name", "credentials_environment_variable"]
+                        "required": ["name", "project_name"]
                     }
                 ]
             }
diff --git a/twined/twine.py b/twined/twine.py
index 5cb2255..4faf357 100644
--- a/twined/twine.py
+++ b/twined/twine.py
@@ -187,7 +187,7 @@ def _validate_manifest(self, kind, source, cls=None, **kwargs):
             data["datasets"] = {dataset["name"]: dataset for dataset in data["datasets"]}
             warnings.warn(
                 message=(
-                    "Datasets belonging to a manifest should be provided as a dictionary mapping their name to"
+                    "Datasets belonging to a manifest should be provided as a dictionary mapping their name to "
                     "themselves. Support for providing a list of datasets will be phased out soon."
                 ),
                 category=DeprecationWarning,