diff --git a/package.json b/package.json
index 4b87f32e..52adae22 100644
--- a/package.json
+++ b/package.json
@@ -62,6 +62,7 @@
     "@types/node": "^14.14.25",
     "@typescript-eslint/eslint-plugin": "^4.28.2",
     "@typescript-eslint/parser": "^4.28.2",
+    "ajv": "^8.11.0",
     "eslint": "^7.30.0",
     "eslint-config-prettier": "^8.3.0",
     "eslint-plugin-import": "^2.23.4",
diff --git a/src/sign-typed-data.test.ts b/src/sign-typed-data.test.ts
index c8e8486a..af858e97 100644
--- a/src/sign-typed-data.test.ts
+++ b/src/sign-typed-data.test.ts
@@ -1,10 +1,12 @@
 import * as ethUtil from 'ethereumjs-util';
+import Ajv from 'ajv';
 import {
   recoverTypedSignature,
   signTypedData,
   TypedDataUtils,
   typedSignatureHash,
   SignTypedDataVersion,
+  TYPED_MESSAGE_SCHEMA,
 } from './sign-typed-data';
 
 const privateKey = Buffer.from(
@@ -12,6 +14,215 @@ const privateKey = Buffer.from(
   'hex',
 );
 
+/**
+ * Get a list of all Solidity types supported by EIP-712.
+ *
+ * @returns A list of all supported Solidity types.
+ */
+function getEip712SolidityTypes() {
+  const types = ['bool', 'address', 'string', 'bytes'];
+  const ints = Array.from(new Array(32)).map(
+    (_, index) => `int${(index + 1) * 8}`,
+  );
+  const uints = Array.from(new Array(32)).map(
+    (_, index) => `uint${(index + 1) * 8}`,
+  );
+  const bytes = Array.from(new Array(32)).map(
+    (_, index) => `bytes${index + 1}`,
+  );
+
+  return [...types, ...ints, ...uints, ...bytes];
+}
+
+const eip712SolidityTypes = getEip712SolidityTypes();
+
+/**
+ * Validate the given message with the typed message schema.
+ *
+ * @param typedMessage - The typed message to validate.
+ * @returns Whether the message is valid.
+ */
+function validateTypedMessageSchema(
+  typedMessage: Record<string, unknown>,
+): boolean {
+  const ajv = new Ajv();
+  const validate = ajv.compile(TYPED_MESSAGE_SCHEMA);
+  return validate(typedMessage);
+}
+
+describe('TYPED_MESSAGE_SCHEMA', () => {
+  it('should match valid typed message', () => {
+    const typedMessage = {
+      domain: {},
+      message: {},
+      primaryType: 'object',
+      types: {
+        EIP712Domain: [],
+      },
+    };
+
+    expect(validateTypedMessageSchema(typedMessage)).toBe(true);
+  });
+
+  it('should allow custom types in addition to domain', () => {
+    const typedMessage = {
+      domain: {},
+      message: {},
+      primaryType: 'Message',
+      types: {
+        EIP712Domain: [],
+        Message: [],
+      },
+    };
+
+    expect(validateTypedMessageSchema(typedMessage)).toBe(true);
+  });
+
+  eip712SolidityTypes.forEach((solidityType) => {
+    it(`should allow custom type to have type of '${solidityType}'`, () => {
+      const typedMessage = {
+        domain: {},
+        message: {},
+        primaryType: 'Message',
+        types: {
+          EIP712Domain: [],
+          Message: [{ name: 'data', type: solidityType }],
+        },
+      };
+
+      expect(validateTypedMessageSchema(typedMessage)).toBe(true);
+    });
+  });
+
+  it('should allow custom type to have a custom type', () => {
+    const typedMessage = {
+      domain: {},
+      message: {},
+      primaryType: 'Message',
+      types: {
+        CustomValue: [{ name: 'value', type: 'string' }],
+        EIP712Domain: [],
+        Message: [{ name: 'data', type: 'CustomValue' }],
+      },
+    };
+
+    expect(validateTypedMessageSchema(typedMessage)).toBe(true);
+  });
+
+  const invalidStrings = [undefined, null, 0, 1, [], {}];
+
+  for (const invalidString of invalidStrings) {
+    // eslint-disable-next-line no-loop-func
+    it(`should disallow a primary type with value '${invalidString}'`, () => {
+      const typedMessage = {
+        domain: {},
+        message: {},
+        primaryType: invalidString,
+        types: {
+          EIP712Domain: [],
+        },
+      };
+
+      expect(validateTypedMessageSchema(typedMessage)).toBe(false);
+    });
+  }
+
+  const invalidObjects = [undefined, null, 0, 1, [], '', 'test'];
+  for (const invalidObject of invalidObjects) {
+    // eslint-disable-next-line no-loop-func
+    it(`should disallow a typed message with value'${invalidObject}'`, () => {
+      expect(validateTypedMessageSchema(invalidObject as any)).toBe(false);
+    });
+
+    // eslint-disable-next-line no-loop-func
+    it(`should disallow a domain with value '${invalidObject}'`, () => {
+      const typedMessage = {
+        domain: invalidObject,
+        message: {},
+        primaryType: 'object',
+        types: {
+          EIP712Domain: [],
+        },
+      };
+
+      expect(validateTypedMessageSchema(typedMessage)).toBe(false);
+    });
+
+    // eslint-disable-next-line no-loop-func
+    it(`should disallow a message with value '${invalidObject}'`, () => {
+      const typedMessage = {
+        domain: {},
+        message: invalidObject,
+        primaryType: 'object',
+        types: {
+          EIP712Domain: [],
+        },
+      };
+
+      expect(validateTypedMessageSchema(typedMessage)).toBe(false);
+    });
+
+    // eslint-disable-next-line no-loop-func
+    it(`should disallow types with value '${invalidObject}'`, () => {
+      const typedMessage = {
+        domain: {},
+        message: {},
+        primaryType: 'object',
+        types: invalidObject,
+      };
+
+      expect(validateTypedMessageSchema(typedMessage)).toBe(false);
+    });
+  }
+
+  it('should require custom type properties to have a name', () => {
+    const typedMessage = {
+      domain: {},
+      message: {},
+      primaryType: 'Message',
+      types: {
+        EIP712Domain: [],
+        Message: [{ type: 'string' }],
+      },
+    };
+
+    expect(validateTypedMessageSchema(typedMessage)).toBe(false);
+  });
+
+  it('should require custom type properties to have a type', () => {
+    const typedMessage = {
+      domain: {},
+      message: {},
+      primaryType: 'Message',
+      types: {
+        EIP712Domain: [],
+        Message: [{ name: 'name' }],
+      },
+    };
+
+    expect(validateTypedMessageSchema(typedMessage)).toBe(false);
+  });
+
+  const invalidTypes = [undefined, null, 0, 1, [], {}];
+
+  for (const invalidType of invalidTypes) {
+    // eslint-disable-next-line no-loop-func
+    it(`should disallow a type of '${invalidType}'`, () => {
+      const typedMessage = {
+        domain: {},
+        message: {},
+        primaryType: 'Message',
+        types: {
+          EIP712Domain: [],
+          Message: [{ name: 'name', type: invalidType }],
+        },
+      };
+
+      expect(validateTypedMessageSchema(typedMessage)).toBe(false);
+    });
+  }
+});
+
 const encodeDataExamples = {
   // dynamic types supported by EIP-712:
   bytes: [10, '10', '0x10', Buffer.from('10', 'utf8')],
diff --git a/src/sign-typed-data.ts b/src/sign-typed-data.ts
index ca85d2cb..61ca1862 100644
--- a/src/sign-typed-data.ts
+++ b/src/sign-typed-data.ts
@@ -100,7 +100,7 @@ export const TYPED_MESSAGE_SCHEMA = {
           type: 'object',
           properties: {
             name: { type: 'string' },
-            type: { type: 'string', enum: getSolidityTypes() },
+            type: { type: 'string' },
           },
           required: ['name', 'type'],
         },
@@ -113,26 +113,6 @@ export const TYPED_MESSAGE_SCHEMA = {
   required: ['types', 'primaryType', 'domain', 'message'],
 };
 
-/**
- * Get a list of all Solidity types.
- *
- * @returns A list of all Solidity types.
- */
-function getSolidityTypes() {
-  const types = ['bool', 'address', 'string', 'bytes'];
-  const ints = Array.from(new Array(32)).map(
-    (_, index) => `int${(index + 1) * 8}`,
-  );
-  const uints = Array.from(new Array(32)).map(
-    (_, index) => `uint${(index + 1) * 8}`,
-  );
-  const bytes = Array.from(new Array(32)).map(
-    (_, index) => `bytes${index + 1}`,
-  );
-
-  return [...types, ...ints, ...uints, ...bytes];
-}
-
 /**
  * Validate that the given value is a valid version string.
  *
diff --git a/yarn.lock b/yarn.lock
index b8ee7e8a..58f80c27 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1005,6 +1005,16 @@ ajv@^8.0.1:
     require-from-string "^2.0.2"
     uri-js "^4.2.2"
 
+ajv@^8.11.0:
+  version "8.11.0"
+  resolved "https://registry.yarnpkg.com/ajv/-/ajv-8.11.0.tgz#977e91dd96ca669f54a11e23e378e33b884a565f"
+  integrity sha512-wGgprdCvMalC0BztXvitD2hC04YffAvtsUn93JbGXYLAtCUO4xd17mCCZQxUOItiBwZvJScWo8NIvQMQ71rdpg==
+  dependencies:
+    fast-deep-equal "^3.1.1"
+    json-schema-traverse "^1.0.0"
+    require-from-string "^2.0.2"
+    uri-js "^4.2.2"
+
 ansi-colors@^4.1.1:
   version "4.1.1"
   resolved "https://registry.yarnpkg.com/ansi-colors/-/ansi-colors-4.1.1.tgz#cbb9ae256bf750af1eab344f229aa27fe94ba348"