diff --git a/packages/common/src/chains.ts b/packages/common/src/chains.ts
index 8aa54fc14a..8a630a9c3d 100644
--- a/packages/common/src/chains.ts
+++ b/packages/common/src/chains.ts
@@ -3,7 +3,7 @@ import type { ChainConfig } from './types.js'
 export const Mainnet: ChainConfig = {
   name: 'mainnet',
   chainId: 1,
-  defaultHardfork: 'cancun',
+  defaultHardfork: 'prague',
   consensus: {
     type: 'pow',
     algorithm: 'ethash',
@@ -116,6 +116,8 @@ export const Mainnet: ChainConfig = {
     {
       name: 'prague',
       block: null,
+      timestamp: '9999999999', // TEMP: placeholder until mainnet timestamp is set
+      // forkHash: '0xFFFFFFFF' // TODO: set correct forkHash once mainnet timestamp is set
     },
     {
       name: 'osaka',
diff --git a/packages/common/src/common.ts b/packages/common/src/common.ts
index 7603f65eb8..9c896750f1 100644
--- a/packages/common/src/common.ts
+++ b/packages/common/src/common.ts
@@ -62,7 +62,7 @@ export class Common {
     this.events = new EventEmitter<CommonEvent>()
 
     this._chainParams = JSON.parse(JSON.stringify(opts.chain)) // copy
-    this.DEFAULT_HARDFORK = this._chainParams.defaultHardfork ?? Hardfork.Cancun
+    this.DEFAULT_HARDFORK = this._chainParams.defaultHardfork ?? Hardfork.Prague
     // Assign hardfork changes in the sequence of the applied hardforks
     this.HARDFORK_CHANGES = this.hardforks().map((hf) => [
       hf.name,
diff --git a/packages/common/test/chains.spec.ts b/packages/common/test/chains.spec.ts
index 61e27ab55c..50d62168df 100644
--- a/packages/common/test/chains.spec.ts
+++ b/packages/common/test/chains.spec.ts
@@ -18,7 +18,7 @@ describe('[Common/Chains]: Initialization / Chain params', () => {
     const c = new Common({ chain: Mainnet })
     assert.equal(c.chainName(), 'mainnet', 'should initialize with chain name')
     assert.equal(c.chainId(), BigInt(1), 'should return correct chain Id')
-    assert.equal(c.hardfork(), Hardfork.Cancun, 'should set hardfork to current default hardfork')
+    assert.equal(c.hardfork(), Hardfork.Prague, 'should set hardfork to current default hardfork')
     assert.equal(
       c.hardfork(),
       c.DEFAULT_HARDFORK,
diff --git a/packages/common/test/customChains.spec.ts b/packages/common/test/customChains.spec.ts
index 34af5b4393..22bf344504 100644
--- a/packages/common/test/customChains.spec.ts
+++ b/packages/common/test/customChains.spec.ts
@@ -4,6 +4,8 @@ import { Common, Hardfork, Mainnet, createCustomCommon } from '../src/index.js'
 
 import { testnetData } from './data/testnet.js'
 
+import type { ChainConfig } from '../src/index.js'
+
 describe('[Common]: Custom chains', () => {
   it('chain -> object: should provide correct access to private network chain parameters', () => {
     const c = new Common({ chain: testnetData, hardfork: Hardfork.Byzantium })
@@ -87,9 +89,9 @@ describe('[Common]: Custom chains', () => {
       },
       Mainnet,
     )
-    // Note: default HF of Common is currently Cancun
+    // Note: default HF of Common is currently Prague
     // Did not pass any "hardfork" param
-    assert.equal(c.hardfork(), Hardfork.Cancun)
+    assert.equal(c.hardfork(), Hardfork.Prague)
     c.setHardforkBy({
       blockNumber: 0,
     })
@@ -108,6 +110,34 @@ describe('[Common]: Custom chains', () => {
     assert.ok(c.isActivatedEIP(2935))
   })
 
+  it('customChain: correctly set default hardfork on custom chain config', () => {
+    const chainConfig: ChainConfig = {
+      name: 'custom',
+      chainId: 123,
+      genesis: {
+        gasLimit: 0,
+        difficulty: 1,
+        nonce: '0x42',
+        extraData: '0x',
+      },
+      hardforks: [
+        {
+          name: 'chainstart',
+          block: 0,
+        },
+      ],
+      bootstrapNodes: [],
+      consensus: {
+        type: 'pos',
+        algorithm: 'casper',
+        casper: {},
+      },
+    }
+    const c = createCustomCommon({ chainId: 123 }, chainConfig)
+    assert.equal(c.hardfork(), c.DEFAULT_HARDFORK)
+    assert.equal(c.hardfork(), Hardfork.Prague)
+  })
+
   it('customHardforks: override params', () => {
     const c = createCustomCommon(
       {
diff --git a/packages/common/test/hardforks.spec.ts b/packages/common/test/hardforks.spec.ts
index 7d3618f4a4..9b078c3e1b 100644
--- a/packages/common/test/hardforks.spec.ts
+++ b/packages/common/test/hardforks.spec.ts
@@ -133,8 +133,8 @@ describe('[Common]: Hardfork logic', () => {
     msg = 'should return correct next HF (mainnet: byzantium -> constantinople)'
     assert.equal(c.nextHardforkBlockOrTimestamp(Hardfork.Byzantium)!, BigInt(7280000), msg)
 
-    msg = 'should return null if next HF is not available (mainnet: cancun -> prague)'
-    assert.equal(c.nextHardforkBlockOrTimestamp(Hardfork.Cancun), null, msg)
+    msg = 'should return null if next HF is not available (mainnet: prague -> osaka)'
+    assert.equal(c.nextHardforkBlockOrTimestamp(Hardfork.Prague), null, msg)
 
     const c2 = new Common({ chain: Goerli, hardfork: Hardfork.Chainstart })
 
@@ -179,11 +179,11 @@ describe('[Common]: Hardfork logic', () => {
     assert.equal(c.hardforkBlock(Hardfork.Berlin)!, BigInt(12244000), msg)
 
     msg = 'should return null for unscheduled hardfork'
-    // developer note: when Shanghai is set,
+    // developer note: when Osaka is set,
     // update this test to next unscheduled hardfork.
     assert.equal(c.hardforkBlock(Hardfork.Cancun), null, msg)
     assert.equal(c.hardforkBlock(Hardfork.Cancun), null, msg)
-    assert.equal(c.nextHardforkBlockOrTimestamp(Hardfork.Cancun), null, msg)
+    assert.equal(c.nextHardforkBlockOrTimestamp(Hardfork.Prague), null, msg)
   })
 
   it('hardforkGteHardfork()', () => {