diff --git a/.github/workflows/foundry.yml b/.github/workflows/foundry.yml
index 05571cba..4c9bca45 100644
--- a/.github/workflows/foundry.yml
+++ b/.github/workflows/foundry.yml
@@ -105,7 +105,7 @@ jobs:
       - uses: ./.github/actions/install-cache
 
       - name: Run local tests on chain ${{ matrix.chain }} in ${{ matrix.type }} mode
-        run: yarn test:forge:local
+        run: yarn test:forge:local --chain matrix.chain
         env:
           FOUNDRY_FUZZ_RUNS: ${{ matrix.fuzz-runs }}
           FOUNDRY_FUZZ_MAX_TEST_REJECTS: ${{ matrix.max-test-rejects }}
diff --git a/test/forge/fork/helpers/ForkTest.sol b/test/forge/fork/helpers/ForkTest.sol
index f8f6ba5c..01865421 100644
--- a/test/forge/fork/helpers/ForkTest.sol
+++ b/test/forge/fork/helpers/ForkTest.sol
@@ -27,8 +27,8 @@ abstract contract ForkTest is CommonTest, Configured {
     MarketParams[] allMarketParams;
 
     function setUp() public virtual override {
-        // Run fork tests on Ethereum by default.
-        if (block.chainid == 31337) vm.chainId(1);
+        require(block.chainid != 31337, "Fork tests must be run on Ethereum (`--chain 1`) or Base (`--chain 8453`).");
+        require(block.chainid == 1 || block.chainid == 8453, "Unsupported chain.");
 
         _loadConfig();