diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
new file mode 100644
index 0000000..30884b3
--- /dev/null
+++ b/.github/workflows/ci.yaml
@@ -0,0 +1,24 @@
+name: Node.js
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [8.x, 10.x, 12.x, 13.x, 14.x]
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v1
+        with:
+          node-version: ${{ matrix.node-version }}
+      - run: npm install
+      - run: npm run build --if-present
+      - run: npm test
+        env:
+          CI: true
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
index 1f864a2..0000000
--- a/.travis.yml
+++ /dev/null
@@ -1,7 +0,0 @@
-language: node_js
-
-node_js:
-- "13"
-- "12
-- "10"
-- "8"
diff --git a/src/ObjectSchema.js b/src/ObjectSchema.js
index 44c3416..db012b1 100644
--- a/src/ObjectSchema.js
+++ b/src/ObjectSchema.js
@@ -267,8 +267,14 @@ const ObjectSchema = ({ schema = initialState, ...options } = {}) => {
       }
       const src = base._getState()
       const extended = merge(src, schema, { arrayMerge: combineMerge })
-      const { valueOf, ...rest } = BaseSchema({ schema: extended, ...options })
-      return { valueOf }
+      const {
+        valueOf,
+        isFluentSchema,
+        FLUENT_SCHEMA,
+        _getState,
+        ...rest
+      } = BaseSchema({ schema: extended, ...options })
+      return { valueOf, isFluentSchema, FLUENT_SCHEMA, _getState }
     },
 
     /**
diff --git a/src/ObjectSchema.test.js b/src/ObjectSchema.test.js
index cdcf7ed..753b71f 100644
--- a/src/ObjectSchema.test.js
+++ b/src/ObjectSchema.test.js
@@ -600,12 +600,17 @@ describe('ObjectSchema', () => {
         .id('base')
         .title('base')
         .additionalProperties(false)
-        .prop('foo', S.string().minLength(5))
+        .prop(
+          'foo',
+          S.string()
+            .minLength(5)
+            .required(true)
+        )
 
       const extended = S.object()
         .id('extended')
         .title('extended')
-        .prop('bar', S.number())
+        .prop('bar', S.string().required())
         .extend(base)
       expect(extended.valueOf()).toEqual({
         $schema: 'http://json-schema.org/draft-07/schema#',
@@ -618,12 +623,14 @@ describe('ObjectSchema', () => {
             minLength: 5,
           },
           bar: {
-            type: 'number',
+            type: 'string',
           },
         },
+        required: ['foo', 'bar'],
         type: 'object',
       })
     })
+
     it('extends a nested schema', () => {
       const base = S.object()
         .id('base')
@@ -743,6 +750,29 @@ describe('ObjectSchema', () => {
         },
       })
     })
+    it('extends a chain of schemas overriding the props', () => {
+      const base = S.object().prop('reason', S.string().title('title'))
+
+      const extended = S.object()
+        .prop('other')
+        .prop('reason', S.string().minLength(1))
+        .extend(base)
+
+      const extendedAgain = S.object()
+        .prop('again')
+        .prop('reason', S.string().minLength(2))
+        .extend(extended)
+
+      expect(extendedAgain.valueOf()).toEqual({
+        $schema: 'http://json-schema.org/draft-07/schema#',
+        type: 'object',
+        properties: {
+          other: {},
+          again: {},
+          reason: { title: 'title', type: 'string', minLength: 2 },
+        },
+      })
+    })
 
     it('throws an error if a schema is not provided', () => {
       expect(() => {
diff --git a/src/utils.js b/src/utils.js
index 71d41e2..cbcf052 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -40,10 +40,10 @@ const combineMerge = (target, source, options) => {
   const destination = target.slice()
 
   source.forEach((item, index) => {
-    const prop = target.find(prop => prop.name === item.name)
+    const prop = target.find(attr => attr.name === item.name)
     if (typeof destination[index] === 'undefined') {
       destination[index] = options.cloneUnlessOtherwiseSpecified(item, options)
-    } else if (prop) {
+    } else if (options.isMergeableObject(prop)) {
       const propIndex = target.findIndex(prop => prop.name === item.name)
       destination[propIndex] = merge(prop, item, options)
     } else if (target.indexOf(item) === -1) {