diff --git a/src/functional.ts b/src/functional.ts
index c11ea00..a1287cb 100644
--- a/src/functional.ts
+++ b/src/functional.ts
@@ -1,4 +1,4 @@
-import {assert} from "./helpers";
+import {validateBytes} from "./helpers";
 import {IBls} from "./interface";
 
 // Returned type is enforced at each implementation's index
@@ -14,8 +14,9 @@ export function functionalInterfaceFactory({
    * @param message
    */
   function sign(secretKey: Uint8Array, message: Uint8Array): Uint8Array {
-    assert(secretKey, "secretKey is null or undefined");
-    assert(message, "message is null or undefined");
+    validateBytes(secretKey, "secretKey");
+    validateBytes(message, "message");
+
     const privateKey = PrivateKey.fromBytes(secretKey);
     return privateKey.sign(message).toBytes();
   }
@@ -45,9 +46,10 @@ export function functionalInterfaceFactory({
    * @param signature
    */
   function verify(publicKey: Uint8Array, message: Uint8Array, signature: Uint8Array): boolean {
-    assert(publicKey, "publicKey is null or undefined");
-    assert(message, "message is null or undefined");
-    assert(signature, "signature is null or undefined");
+    validateBytes(publicKey, "publicKey");
+    validateBytes(message, "message");
+    validateBytes(signature, "signature");
+
     try {
       return Signature.fromBytes(signature).verify(PublicKey.fromBytes(publicKey), message);
     } catch (e) {
@@ -62,9 +64,10 @@ export function functionalInterfaceFactory({
    * @param signature
    */
   function verifyAggregate(publicKeys: Uint8Array[], message: Uint8Array, signature: Uint8Array): boolean {
-    assert(publicKeys, "publicKey is null or undefined");
-    assert(message, "message is null or undefined");
-    assert(signature, "signature is null or undefined");
+    validateBytes(publicKeys, "publicKey");
+    validateBytes(message, "message");
+    validateBytes(signature, "signature");
+
     try {
       return Signature.fromBytes(signature).verifyAggregate(
         publicKeys.map((pubkey) => PublicKey.fromBytes(pubkey)),
@@ -83,9 +86,9 @@ export function functionalInterfaceFactory({
    * @param fast Check if all messages are different
    */
   function verifyMultiple(publicKeys: Uint8Array[], messages: Uint8Array[], signature: Uint8Array): boolean {
-    assert(publicKeys, "publicKey is null or undefined");
-    assert(messages, "message is null or undefined");
-    assert(signature, "signature is null or undefined");
+    validateBytes(publicKeys, "publicKey");
+    validateBytes(messages, "message");
+    validateBytes(signature, "signature");
 
     if (publicKeys.length === 0 || publicKeys.length != messages.length) {
       return false;
diff --git a/src/helpers/utils.ts b/src/helpers/utils.ts
index a724b0d..6a7c143 100644
--- a/src/helpers/utils.ts
+++ b/src/helpers/utils.ts
@@ -3,12 +3,6 @@ import randomBytes from "randombytes";
 // Single import to ease changing this lib if necessary
 export {randomBytes};
 
-export function assert(condition: unknown, message = "Assertion failed"): asserts condition {
-  if (!condition) {
-    throw new Error(message);
-  }
-}
-
 export function isEqualBytes(a: Buffer | Uint8Array, b: Buffer | Uint8Array): boolean {
   return toBuffer(a).equals(toBuffer(b));
 }
@@ -16,3 +10,17 @@ export function isEqualBytes(a: Buffer | Uint8Array, b: Buffer | Uint8Array): bo
 export function toBuffer(input: Uint8Array): Buffer {
   return Buffer.from(input.buffer, input.byteOffset, input.length);
 }
+
+/**
+ * Validate bytes to prevent confusing WASM errors downstream if bytes is null
+ */
+export function validateBytes(
+  bytes: Uint8Array | Uint8Array[] | null,
+  argName?: string
+): asserts bytes is NonNullable<typeof bytes> {
+  for (const item of Array.isArray(bytes) ? bytes : [bytes]) {
+    if (item == null) {
+      throw Error(`${argName || "bytes"} is null or undefined`);
+    }
+  }
+}