diff --git a/compose/config/fields_schema.json b/compose/config/fields_schema.json
index 6277b57d69..baf7eb0eec 100644
--- a/compose/config/fields_schema.json
+++ b/compose/config/fields_schema.json
@@ -36,7 +36,15 @@
 
         "environment": {
           "oneOf": [
-            {"type": "object"},
+            {
+              "type": "object",
+              "patternProperties": {
+                "^[a-zA-Z0-9_]+$": {
+                  "type": ["string", "number"]
+                }
+              },
+              "additionalProperties": false
+            },
             {"type": "array", "items": {"type": "string"}, "uniqueItems": true}
           ]
         },
diff --git a/docs/yml.md b/docs/yml.md
index 9c1ffa07a4..17415684db 100644
--- a/docs/yml.md
+++ b/docs/yml.md
@@ -184,17 +184,21 @@ Mount all of the volumes from another service or container.
 
 ### environment
 
-Add environment variables. You can use either an array or a dictionary.
+Add environment variables. You can use either an array or a dictionary. Any
+boolean values; true, false, yes no, need to be enclosed in quotes to ensure
+they are not converted to True or False by the YML parser.
 
 Environment variables with only a key are resolved to their values on the
 machine Compose is running on, which can be helpful for secret or host-specific values.
 
     environment:
       RACK_ENV: development
+      SHOW: 'true'
       SESSION_SECRET:
 
     environment:
       - RACK_ENV=development
+      - SHOW=true
       - SESSION_SECRET
 
 ### env_file
diff --git a/tests/unit/config_test.py b/tests/unit/config_test.py
index f55789207d..0c1f81baa6 100644
--- a/tests/unit/config_test.py
+++ b/tests/unit/config_test.py
@@ -270,15 +270,15 @@ class ConfigTest(unittest.TestCase):
             )
             self.assertEqual(service[0]['entrypoint'], entrypoint)
 
-    def test_validation_message_for_invalid_type_when_multiple_types_allowed(self):
-        expected_error_msg = "Service 'web' configuration key 'mem_limit' contains an invalid type, it should be a number or a string"
+    def test_config_environment_contains_boolean_validation_error(self):
+        expected_error_msg = "Service 'web' configuration key 'environment' contains an invalid type"
 
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
                 config.ConfigDetails(
                     {'web': {
                         'image': 'busybox',
-                        'mem_limit': ['incorrect']
+                        'environment': {'SHOW_STUFF': True}
                     }},
                     'working_dir',
                     'filename.yml'