diff --git a/apps/web/src/components/specification/decoder.ts b/apps/web/src/components/specification/decoder.ts
index 70df7109..77e3554e 100644
--- a/apps/web/src/components/specification/decoder.ts
+++ b/apps/web/src/components/specification/decoder.ts
@@ -21,6 +21,7 @@ import {
     decodeFunctionData,
     parseAbiParameters,
     slice,
+    SliceOffsetOutOfBoundsError,
 } from "viem";
 import SpecificationModeNotSupportedError from "./errors/SpecificationModeNotSupported";
 import { ABI_PARAMS, JSON_ABI, Specification, specModes } from "./types";
@@ -70,8 +71,28 @@ const addPiecesToEnvelope = (e: Envelope): Envelope => {
         try {
             if (e.spec.sliceInstructions?.length) {
                 e.spec.sliceInstructions.forEach((instruction, index) => {
-                    const { from, to, name, type } = instruction;
-                    const part = slice(e.input, from, to);
+                    const {
+                        from,
+                        to,
+                        name,
+                        type,
+                        optional = false,
+                    } = instruction;
+                    let part;
+
+                    try {
+                        part = slice(e.input, from, to);
+                    } catch (err: any) {
+                        if (
+                            err instanceof SliceOffsetOutOfBoundsError &&
+                            optional
+                        ) {
+                            part = "0x" as Hex;
+                        } else {
+                            throw err;
+                        }
+                    }
+
                     const decodedPart =
                         !isNil(type) && !isEmpty(type)
                             ? head(decodeAbiParameters([{ type, name }], part))
diff --git a/apps/web/src/components/specification/systemSpecs.ts b/apps/web/src/components/specification/systemSpecs.ts
index 619cf848..2d4f8fc0 100644
--- a/apps/web/src/components/specification/systemSpecs.ts
+++ b/apps/web/src/components/specification/systemSpecs.ts
@@ -85,6 +85,7 @@ const ERC20PortalSpec: Specification = {
         { from: 1, to: 21, name: "tokenAddress" },
         { from: 21, to: 41, name: "from" },
         { from: 41, to: 73, name: "amount", type: "uint" },
+        { from: 73, name: "execLayerData", optional: true },
     ],
     abiParams: [],
     conditionals: [
@@ -135,6 +136,7 @@ const EtherPortalSpec: Specification = {
     sliceInstructions: [
         { from: 0, to: 20, name: "sender" },
         { from: 20, to: 52, name: "amount", type: "uint256" },
+        { from: 52, name: "execLayerData", optional: true },
     ],
     abiParams: [],
     conditionals: [
diff --git a/apps/web/src/components/specification/types.ts b/apps/web/src/components/specification/types.ts
index 641dd8a3..1309a9bf 100644
--- a/apps/web/src/components/specification/types.ts
+++ b/apps/web/src/components/specification/types.ts
@@ -46,6 +46,8 @@ export interface SliceInstruction {
     name?: string;
     /** The type to decode e.g. uint. Leaving empty will default to the raw sliced return; useful for Address for example.*/
     type?: AbiType;
+    /** A flag to signal to the decoder not to throw an exception caused by slicing the defined byte range.*/
+    optional?: boolean;
 }
 
 type Commons = {
diff --git a/apps/web/test/components/specification/decoder.test.ts b/apps/web/test/components/specification/decoder.test.ts
index 408ca660..5dc9c4d6 100644
--- a/apps/web/test/components/specification/decoder.test.ts
+++ b/apps/web/test/components/specification/decoder.test.ts
@@ -229,8 +229,44 @@ Slice name: "from" (Is it the right one?)`,
                 expect(envelope.result).toEqual({
                     amount: 10000000000000000n,
                     sender: "0x0c70e9a737aa92055c8c1217bf887a65cb2292f4",
+                    execLayerData: "0x",
                 });
             });
+
+            it("should decode ether-portal data with the exec-layer information", () => {
+                const envelope = decodePayload(
+                    systemSpecification.EtherPortalSpec,
+                    encodedDataSamples.etherPortalSampleWithExecLayer,
+                );
+
+                expect(envelope.result).toEqual({
+                    amount: 300n,
+                    execLayerData:
+                        "0x33303020657468206465706f736974656420746f20307833613134363931353532376264313532383032366235633134333335303938646666323730306361",
+                    sender: "0x3a146915527bd1528026b5c14335098dff2700ca",
+                });
+            });
+
+            it("should fail to decode ether-portal data with required but missing exec-layer information", () => {
+                const envelope = decodePayload(
+                    {
+                        ...systemSpecification.EtherPortalSpec,
+                        sliceInstructions:
+                            systemSpecification.EtherPortalSpec.sliceInstructions?.map(
+                                (instruction) =>
+                                    instruction.name === "execLayerData"
+                                        ? {
+                                              ...instruction,
+                                              optional: false,
+                                          }
+                                        : instruction,
+                            ),
+                    },
+                    encodedDataSamples.etherPortalSampleWithoutExecLayer,
+                );
+
+                expect(envelope.result).toEqual({});
+            });
         });
 
         describe("Struct definition example cases", () => {