diff --git a/package.json b/package.json
index 0e50ce1..b63b1ac 100644
--- a/package.json
+++ b/package.json
@@ -29,6 +29,7 @@
   },
   "scripts": {
     "lint": "standard | snazzy",
+    "lint:fix": "standard --fix",
     "test": "npm run test:unit && npm run test:typescript",
     "test:unit": "jest --coverage",
     "test:watch": "jest src/*.test.js --verbose --watch",
diff --git a/src/BaseSchema.test.js b/src/BaseSchema.test.js
index 5157d5e..56790c6 100644
--- a/src/BaseSchema.test.js
+++ b/src/BaseSchema.test.js
@@ -548,7 +548,10 @@ describe('BaseSchema', () => {
         ).toEqual({
           $schema: 'http://json-schema.org/draft-07/schema#',
           properties: {
-            prop: { anyOf: [{ type: 'string' }, { type: 'null' }] }
+            prop: {
+              type: ['string', 'null'],
+              anyOf: [{ type: 'string' }, { type: 'null' }]
+            }
           },
           type: 'object'
         })
diff --git a/src/FluentSchema.integration.test.js b/src/FluentSchema.integration.test.js
index daf6a41..c034704 100644
--- a/src/FluentSchema.integration.test.js
+++ b/src/FluentSchema.integration.test.js
@@ -224,7 +224,9 @@ describe('S', () => {
   })
 
   describe('compose keywords', () => {
-    const ajv = new Ajv()
+    const ajv = new Ajv({
+      allowUnionTypes: true
+    })
     const schema = S.object()
       .prop('foo', S.anyOf([S.string()]))
       .prop('bar', S.not(S.anyOf([S.integer()])))
diff --git a/src/FluentSchema.test.js b/src/FluentSchema.test.js
index e20144e..2809e61 100644
--- a/src/FluentSchema.test.js
+++ b/src/FluentSchema.test.js
@@ -202,13 +202,24 @@ describe('S', () => {
   })
 
   describe('composition', () => {
+    it('anyOf', () => {
+      const schema = S.object()
+        .prop('foo', S.string().anyOf([S.string()]))
+        .valueOf()
+      expect(schema).toEqual({
+        $schema: 'http://json-schema.org/draft-07/schema#',
+        properties: { foo: { type: 'string', anyOf: [{ type: 'string' }] } },
+        type: 'object'
+      })
+    })
+
     it('anyOf', () => {
       const schema = S.object()
         .prop('foo', S.anyOf([S.string()]))
         .valueOf()
       expect(schema).toEqual({
         $schema: 'http://json-schema.org/draft-07/schema#',
-        properties: { foo: { anyOf: [{ type: 'string' }] } },
+        properties: { foo: { type: 'string', anyOf: [{ type: 'string' }] } },
         type: 'object'
       })
     })
@@ -225,6 +236,7 @@ describe('S', () => {
         $schema: 'http://json-schema.org/draft-07/schema#',
         properties: {
           multipleRestrictedTypesKey: {
+            type: ['string', 'number'],
             oneOf: [{ type: 'string' }, { minimum: 10, type: 'number' }]
           },
           notTypeKey: { not: { oneOf: [{ pattern: 'js$', type: 'string' }] } }
diff --git a/src/ObjectSchema.js b/src/ObjectSchema.js
index 26bf978..4965b91 100644
--- a/src/ObjectSchema.js
+++ b/src/ObjectSchema.js
@@ -8,7 +8,8 @@ const {
   patchIdsWithParentId,
   appendRequired,
   FluentSchemaError,
-  combineDeepmerge
+  combineDeepmerge,
+  getCombinedType
 } = require('./utils')
 
 const initialState = {
@@ -303,7 +304,7 @@ const ObjectSchema = ({ schema = initialState, ...options } = {}) => {
       }
 
       const type = hasCombiningKeywords(attributes)
-        ? undefined
+        ? getCombinedType(attributes)
         : attributes.type
 
       // strip undefined values or empty arrays or internals
diff --git a/src/utils.js b/src/utils.js
index 40446b5..f44e86b 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -5,6 +5,38 @@ const isFluentSchema = obj => obj && obj.isFluentSchema
 const hasCombiningKeywords = attributes =>
   attributes.allOf || attributes.anyOf || attributes.oneOf || attributes.not
 
+const getCombinedType = (attributes) => {
+  const resultSet = new Set()
+
+  if (attributes.type) {
+    resultSet.add(attributes.type)
+  }
+
+  if (attributes.allOf) {
+    for (const item of attributes.allOf) {
+      resultSet.add(item.type)
+    }
+  }
+
+  if (attributes.anyOf) {
+    for (const item of attributes.anyOf) {
+      resultSet.add(item.type)
+    }
+  }
+
+  if (attributes.oneOf) {
+    for (const item of attributes.oneOf) {
+      resultSet.add(item.type)
+    }
+  }
+
+  if (resultSet.size === 1) {
+    return [...resultSet][0]
+  }
+
+  return [...resultSet]
+}
+
 class FluentSchemaError extends Error {
   constructor (message) {
     super(message)
@@ -224,6 +256,7 @@ const setComposeType = ({ prop, schemas, schema, options }) => {
 
 module.exports = {
   isFluentSchema,
+  getCombinedType,
   hasCombiningKeywords,
   FluentSchemaError,
   last,