diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index b94c1715..b84ca88e 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -12,6 +12,7 @@ on:
     branches:
       - main
       - develop
+      - feature/fork-etrog
 
 jobs:
   build:
diff --git a/src/constants.js b/src/constants.js
index 7e9126e2..81e54a6b 100644
--- a/src/constants.js
+++ b/src/constants.js
@@ -80,5 +80,8 @@ module.exports.DELTA_TIMESTAMP_BYTES = 4;
 module.exports.INDEX_L1INFOTREE_BYTES = 4;
 module.exports.TYPE_BYTES = 1;
 
+// Bridge
+module.exports.GLOBAL_INDEX_MAINNET_FLAG = Scalar.pow(2, 64);
+
 // Common
 module.exports.ZERO_BYTES32 = '0x0000000000000000000000000000000000000000000000000000000000000000';
diff --git a/src/mt-bridge-utils.js b/src/mt-bridge-utils.js
index ac78f433..6f8b1a24 100644
--- a/src/mt-bridge-utils.js
+++ b/src/mt-bridge-utils.js
@@ -1,4 +1,6 @@
 const ethers = require('ethers');
+const { Scalar } = require('ffjavascript');
+const Constants = require('./constants');
 
 /**
  * Calculate an array zero hashes of
@@ -51,8 +53,26 @@ function getLeafValue(leafType, originNetwork, originAddress, destinationNetwork
     return ethers.utils.solidityKeccak256(['uint8', 'uint32', 'address', 'uint32', 'address', 'uint256', 'bytes32'], [leafType, originNetwork, originAddress, destinationNetwork, destinationAddress, amount, metadataHash]);
 }
 
+/**
+ * Compute globalIndex
+ * | 191 bits |    1 bit     |   32 bits   |  32 bits   |
+ * |    0     |  mainnetFlag | indexRollup | indexLocal |
+ * @param {Number | BigInt} indexLocal - leaf index on the mainnet exit tree
+ * @param {Number | BigInt} indexRollup - leaf index on the rollup tree
+ * @param {Bool} isMainnet flag that indicates if it is mainnet
+ * @returns {BigInt} global index
+ */
+function computeGlobalIndex(indexLocal, indexRollup, isMainnet) {
+    if (isMainnet === true) {
+        return Scalar.add(indexLocal, Constants.GLOBAL_INDEX_MAINNET_FLAG);
+    }
+
+    return Scalar.add(indexLocal, Scalar.mul(indexRollup, Scalar.pow(2, 32)));
+}
+
 module.exports = {
     generateZeroHashes,
     verifyMerkleProof,
     getLeafValue,
+    computeGlobalIndex,
 };
diff --git a/test/helpers/test-vectors/merkle-tree-bridge/global-index.json b/test/helpers/test-vectors/merkle-tree-bridge/global-index.json
new file mode 100644
index 00000000..dd9b8f6b
--- /dev/null
+++ b/test/helpers/test-vectors/merkle-tree-bridge/global-index.json
@@ -0,0 +1,50 @@
+[
+  {
+    "indexLocal": "0",
+    "indexRollup": "0",
+    "isMainnet": false,
+    "expectedGlobalIndex": "0"
+  },
+  {
+    "indexLocal": "0",
+    "indexRollup": "0",
+    "isMainnet": true,
+    "expectedGlobalIndex": "18446744073709551616"
+  },
+  {
+    "indexLocal": "1",
+    "indexRollup": "0",
+    "isMainnet": false,
+    "expectedGlobalIndex": "1"
+  },
+  {
+    "indexLocal": "1",
+    "indexRollup": "0",
+    "isMainnet": true,
+    "expectedGlobalIndex": "18446744073709551617"
+  },
+  {
+    "indexLocal": "0",
+    "indexRollup": "1",
+    "isMainnet": false,
+    "expectedGlobalIndex": "4294967296"
+  },
+  {
+    "indexLocal": "0",
+    "indexRollup": "1",
+    "isMainnet": true,
+    "expectedGlobalIndex": "18446744073709551616"
+  },
+  {
+    "indexLocal": "18446744073709551615",
+    "indexRollup": "18446744073709551615",
+    "isMainnet": false,
+    "expectedGlobalIndex": "79228162532711081662958534655"
+  },
+  {
+    "indexLocal": "18446744073709551615",
+    "indexRollup": "18446744073709551615",
+    "isMainnet": true,
+    "expectedGlobalIndex": "36893488147419103231"
+  }
+]
\ No newline at end of file
diff --git a/test/mt-bridge-utils.test.js b/test/mt-bridge-utils.test.js
new file mode 100644
index 00000000..1d519a0c
--- /dev/null
+++ b/test/mt-bridge-utils.test.js
@@ -0,0 +1,45 @@
+const fs = require('fs');
+const path = require('path');
+const { Scalar } = require('ffjavascript');
+const { expect } = require('chai');
+const { argv } = require('yargs');
+const {
+    computeGlobalIndex,
+} = require('../index').mtBridgeUtils;
+const { pathTestVectors } = require('./helpers/test-utils');
+
+describe('Merkle Bridge Utils', () => {
+    const pathTests = path.join(pathTestVectors, 'merkle-tree-bridge/global-index.json');
+
+    let update;
+    let testVectors;
+
+    before(async () => {
+        testVectors = JSON.parse(fs.readFileSync(pathTests));
+        update = argv.update === true;
+    });
+
+    it('computeGlobalIndex', async () => {
+        for (let i = 0; i < testVectors.length; i++) {
+            const {
+                indexLocal, indexRollup, isMainnet, expectedGlobalIndex,
+            } = testVectors[i];
+
+            const computedGlobalIndex = computeGlobalIndex(
+                Scalar.e(indexLocal),
+                Scalar.e(indexRollup),
+                isMainnet,
+            );
+
+            if (update) {
+                testVectors[i].expectedGlobalIndex = computedGlobalIndex.toString();
+            } else {
+                expect(computedGlobalIndex.toString()).to.be.equal(expectedGlobalIndex);
+            }
+        }
+
+        if (update) {
+            fs.writeFileSync(pathTests, JSON.stringify(testVectors, null, 2));
+        }
+    });
+});