diff --git a/packages/@aws-cdk/cloudformation-include/test/test-templates/yaml/year-month-date-as-strings.yaml b/packages/@aws-cdk/cloudformation-include/test/test-templates/yaml/year-month-date-as-strings.yaml
new file mode 100644
index 0000000000000..f25f363879810
--- /dev/null
+++ b/packages/@aws-cdk/cloudformation-include/test/test-templates/yaml/year-month-date-as-strings.yaml
@@ -0,0 +1,14 @@
+AWSTemplateFormatVersion: 2010-09-09
+Resources:
+  Role:
+    Type: AWS::IAM::Role
+    Properties:
+      AssumeRolePolicyDocument:
+        Version: 2012-10-17
+        Statement:
+          - Effect: Allow
+            Principal:
+              Service:
+                - ec2.amazonaws.com
+            Action:
+              - sts:AssumeRole
diff --git a/packages/@aws-cdk/cloudformation-include/test/yaml-templates.test.ts b/packages/@aws-cdk/cloudformation-include/test/yaml-templates.test.ts
index 5faf8bd1a5e1c..0724020f90f56 100644
--- a/packages/@aws-cdk/cloudformation-include/test/yaml-templates.test.ts
+++ b/packages/@aws-cdk/cloudformation-include/test/yaml-templates.test.ts
@@ -23,6 +23,33 @@ describe('CDK Include', () => {
     );
   });
 
+  test('can ingest a template with year-month-date parsed as string instead of Date', () => {
+    includeTestTemplate(stack, 'year-month-date-as-strings.yaml');
+
+    expect(stack).toMatchTemplate({
+      "AWSTemplateFormatVersion": "2010-09-09",
+      "Resources": {
+        "Role": {
+          "Type": "AWS::IAM::Role",
+          "Properties": {
+            "AssumeRolePolicyDocument": {
+              "Version": "2012-10-17",
+              "Statement": [
+                {
+                  "Effect": "Allow",
+                  "Principal": {
+                    "Service": ["ec2.amazonaws.com"],
+                  },
+                  "Action": ["sts:AssumeRole"],
+                },
+              ],
+            },
+          },
+        },
+      },
+    });
+  });
+
   test('can ingest a template with the short form Base64 function', () => {
     includeTestTemplate(stack, 'short-form-base64.yaml');
 
diff --git a/packages/@aws-cdk/yaml-cfn/lib/yaml.ts b/packages/@aws-cdk/yaml-cfn/lib/yaml.ts
index eca37db0ed048..e46c8f8d6bf72 100644
--- a/packages/@aws-cdk/yaml-cfn/lib/yaml.ts
+++ b/packages/@aws-cdk/yaml-cfn/lib/yaml.ts
@@ -54,6 +54,6 @@ const shortForms: yaml_types.Schema.CustomTag[] = [
 function parseYamlStrWithCfnTags(text: string): any {
   return yaml.parse(text, {
     customTags: shortForms,
-    schema: 'yaml-1.1',
+    schema: 'core',
   });
 }
diff --git a/packages/@aws-cdk/yaml-cfn/test/deserialization.test.ts b/packages/@aws-cdk/yaml-cfn/test/deserialization.test.ts
new file mode 100644
index 0000000000000..e2a3688393b61
--- /dev/null
+++ b/packages/@aws-cdk/yaml-cfn/test/deserialization.test.ts
@@ -0,0 +1,34 @@
+import '@aws-cdk/assert/jest';
+import * as yaml_cfn from '../lib';
+
+test('Unquoted year-month-day is treated as a string, not a Date', () => {
+  const value = yaml_cfn.deserialize('Key: 2020-12-31');
+
+  expect(value).toEqual({
+    Key: '2020-12-31',
+  });
+});
+
+test("Unquoted 'No' is treated as a string, not a boolean", () => {
+  const value = yaml_cfn.deserialize('Key: No');
+
+  expect(value).toEqual({
+    Key: 'No',
+  });
+});
+
+test("Short-form 'Ref' is deserialized correctly", () => {
+  const value = yaml_cfn.deserialize('!Ref Resource');
+
+  expect(value).toEqual({
+    Ref: 'Resource',
+  });
+});
+
+test("Short-form 'Fn::GetAtt' is deserialized correctly", () => {
+  const value = yaml_cfn.deserialize('!GetAtt Resource.Attribute');
+
+  expect(value).toEqual({
+    'Fn::GetAtt': 'Resource.Attribute',
+  });
+});
diff --git a/packages/@aws-cdk/yaml-cfn/test/serialization.test.ts b/packages/@aws-cdk/yaml-cfn/test/serialization.test.ts
new file mode 100644
index 0000000000000..bbc3a45d6ac26
--- /dev/null
+++ b/packages/@aws-cdk/yaml-cfn/test/serialization.test.ts
@@ -0,0 +1,8 @@
+import '@aws-cdk/assert/jest';
+import * as yaml_cfn from '../lib';
+
+test('An object with a single string value is serialized as a simple string', () => {
+  const value = yaml_cfn.serialize({ key: 'some string' });
+
+  expect(value).toEqual('key: some string\n');
+});
diff --git a/packages/@aws-cdk/yaml-cfn/test/yaml.test.ts b/packages/@aws-cdk/yaml-cfn/test/yaml.test.ts
deleted file mode 100644
index f8ce8131c4de7..0000000000000
--- a/packages/@aws-cdk/yaml-cfn/test/yaml.test.ts
+++ /dev/null
@@ -1,5 +0,0 @@
-import '@aws-cdk/assert/jest';
-
-test('No tests are specified for this package', () => {
-  expect(true).toBe(true);
-});