diff --git a/packages/util-crypto/src/nacl/convertKey.spec.ts b/packages/util-crypto/src/nacl/convertKey.spec.ts
new file mode 100644
index 000000000..2ed8acdf0
--- /dev/null
+++ b/packages/util-crypto/src/nacl/convertKey.spec.ts
@@ -0,0 +1,36 @@
+// Copyright 2017-2021 @polkadot/util-crypto authors & contributors
+// SPDX-License-Identifier: Apache-2.0
+
+import { u8aToHex } from '@polkadot/util';
+
+import { convertPublicKeyToCurve25519, convertSecretKeyToCurve25519 } from '.';
+
+describe('convertPublicKeyToCurve25519', (): void => {
+  it('converts a known key correctly', (): void => {
+    expect(
+      u8aToHex(convertPublicKeyToCurve25519(
+        new Uint8Array([
+          180, 114, 93, 155, 165, 255, 217, 82,
+          16, 250, 209, 11, 193, 10, 88, 218,
+          190, 190, 41, 193, 236, 252, 1, 152,
+          216, 214, 0, 41, 45, 138, 13, 53
+        ])
+      ))
+    ).toEqual('0x5e05848ceeef4f306d6e285a26faf1a8070cf0c89f8d28ab966002fe4ad17746');
+  });
+});
+
+describe('convertSecretKeyToCurve25519', (): void => {
+  it('converts a known key correctly', (): void => {
+    expect(
+      u8aToHex(convertSecretKeyToCurve25519(
+        new Uint8Array([
+          1, 2, 3, 4, 5, 6, 7, 8,
+          1, 2, 3, 4, 5, 6, 7, 8,
+          1, 2, 3, 4, 5, 6, 7, 8,
+          1, 2, 3, 4, 5, 6, 7, 8
+        ])
+      ))
+    ).toEqual('0xd875a82940b9174dabb1c0c895485810cc2870f5808565b59d4ef708bdcf526c');
+  });
+});
diff --git a/packages/util-crypto/src/nacl/convertKey.ts b/packages/util-crypto/src/nacl/convertKey.ts
index 2cdf48022..19e0cb667 100644
--- a/packages/util-crypto/src/nacl/convertKey.ts
+++ b/packages/util-crypto/src/nacl/convertKey.ts
@@ -3,10 +3,12 @@
 
 import ed2curve from 'ed2curve';
 
+import { assertReturn } from '@polkadot/util';
+
 export function convertSecretKeyToCurve25519 (secretKey: Uint8Array): Uint8Array {
   return ed2curve.convertSecretKey(secretKey);
 }
 
 export function convertPublicKeyToCurve25519 (publicKey: Uint8Array): Uint8Array {
-  return ed2curve.convertPublicKey(publicKey) as Uint8Array;
+  return assertReturn(ed2curve.convertPublicKey(publicKey), 'Unable to convert publicKey to ed25519');
 }
diff --git a/packages/util-crypto/src/pbkdf2/encode.spec.ts b/packages/util-crypto/src/pbkdf2/encode.spec.ts
index 6777c527b..f093d9211 100644
--- a/packages/util-crypto/src/pbkdf2/encode.spec.ts
+++ b/packages/util-crypto/src/pbkdf2/encode.spec.ts
@@ -7,7 +7,12 @@ import { waitReady } from '@polkadot/wasm-crypto';
 import { randomAsU8a } from '../random/asU8a';
 import { pbkdf2Encode } from '.';
 
-const KNOWN_SALT = new Uint8Array([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32]);
+const KNOWN_SALT = new Uint8Array([
+  1, 2, 3, 4, 5, 6, 7, 8,
+  9, 10, 11, 12, 13, 14, 15, 16,
+  17, 18, 19, 20, 21, 22, 23, 24,
+  25, 26, 27, 28, 29, 30, 31, 32
+]);
 const TEST_PASSWORD = 'test password';
 
 describe('pbkdf2Encode', (): void => {
diff --git a/packages/util/src/assert.spec.ts b/packages/util/src/assert.spec.ts
index 2a8cb30e6..e7a5ec93e 100644
--- a/packages/util/src/assert.spec.ts
+++ b/packages/util/src/assert.spec.ts
@@ -10,13 +10,13 @@ describe('assert', (): void => {
 
   it('should throw an error when test is not true', (): void => {
     expect(
-      (): void => assert(false, 'error thrown')
+      () => assert(false, 'error thrown')
     ).toThrow(/error thrown/);
   });
 
   it('should throw an error when message: () => string', (): void => {
     expect(
-      (): void => assert(false, (): string => 'message from function')
+      () => assert(false, (): string => 'message from function')
     ).toThrow(/message from function/);
   });
 });
diff --git a/packages/util/src/assert.ts b/packages/util/src/assert.ts
index 59db28dee..5991c89b5 100644
--- a/packages/util/src/assert.ts
+++ b/packages/util/src/assert.ts
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 import { isFunction } from './is/function';
+import { isNull } from './is/null';
 import { isUndefined } from './is/undefined';
 
 type MessageFn = () => string;
@@ -36,8 +37,8 @@ export function assert (condition: unknown, message: string | MessageFn): assert
  * @name assertReturn
  * @summart Returns when the value is not undefined, otherwise throws assertion error
  */
-export function assertReturn <T> (value: T | undefined, message: string | MessageFn): T {
-  assert(!isUndefined(value), message);
+export function assertReturn <T> (value: T | undefined | null, message: string | MessageFn): T {
+  assert(!isUndefined(value) && !isNull(value), message);
 
   return value;
 }