diff --git a/web3.js/src/ed25519-program.ts b/web3.js/src/ed25519-program.ts
index fab806ea8a..b990a06ab7 100644
--- a/web3.js/src/ed25519-program.ts
+++ b/web3.js/src/ed25519-program.ts
@@ -30,7 +30,19 @@ export type CreateEd25519InstructionWithPrivateKeyParams = {
   instructionIndex?: number;
 };
 
-const ED25519_INSTRUCTION_LAYOUT = BufferLayout.struct([
+const ED25519_INSTRUCTION_LAYOUT = BufferLayout.struct<
+  Readonly<{
+    messageDataOffset: number;
+    messageDataSize: number;
+    messageInstructionIndex: number;
+    numSignatures: number;
+    padding: number;
+    publicKeyInstructionIndex: number;
+    publicKeyOffset: number;
+    signatureInstructionIndex: number;
+    signatureOffset: number;
+  }>
+>([
   BufferLayout.u8('numSignatures'),
   BufferLayout.u8('padding'),
   BufferLayout.u16('signatureOffset'),
@@ -82,17 +94,18 @@ export class Ed25519Program {
 
     const instructionData = Buffer.alloc(messageDataOffset + message.length);
 
+    const index = instructionIndex != null ? instructionIndex : 0;
     ED25519_INSTRUCTION_LAYOUT.encode(
       {
         numSignatures,
         padding: 0,
         signatureOffset,
-        signatureInstructionIndex: instructionIndex,
+        signatureInstructionIndex: index,
         publicKeyOffset,
-        publicKeyInstructionIndex: instructionIndex,
+        publicKeyInstructionIndex: index,
         messageDataOffset,
         messageDataSize: message.length,
-        messageInstructionIndex: instructionIndex,
+        messageInstructionIndex: index,
       },
       instructionData,
     );