diff --git a/.changeset/tempo-testnet-hardfork-t5.md b/.changeset/tempo-testnet-hardfork-t5.md
new file mode 100644
index 0000000000..49c17bc8fa
--- /dev/null
+++ b/.changeset/tempo-testnet-hardfork-t5.md
@@ -0,0 +1,5 @@
+---
+"viem": patch
+---
+
+**Tempo:** Set the `t5` hardfork on the Tempo Testnet (Moderato) chain.
diff --git a/src/chains/definitions/tempoModerato.ts b/src/chains/definitions/tempoModerato.ts
index 4949bfa879..b08c50d119 100644
--- a/src/chains/definitions/tempoModerato.ts
+++ b/src/chains/definitions/tempoModerato.ts
@@ -4,6 +4,7 @@ import { defineChain } from '../../utils/chain/defineChain.js'
 export const tempoModerato = /*#__PURE__*/ defineChain({
   ...chainConfig,
   id: 42431,
+  hardfork: 't5',
   blockExplorers: {
     default: {
       name: 'Tempo Explorer',