diff --git a/tests/test_uniswap4.py b/tests/test_uniswap4.py
index 22cbaf4..864d4d4 100644
--- a/tests/test_uniswap4.py
+++ b/tests/test_uniswap4.py
@@ -1,10 +1,11 @@
 import logging
 import os
 import shutil
+import socket
 import subprocess
+import time
 from contextlib import contextmanager
 from dataclasses import astuple, dataclass
-from time import sleep
 from typing import Generator, List, Optional
 
 import pytest
@@ -118,7 +119,23 @@ def anvil() -> Generator[AnvilInstance, None, None]:
     # Address #1 when anvil is run with `--wallet.seed test`, it starts with 1000 ETH
     eth_address = "0xa0Ee7A142d267C1f36714E4a8F75612F20a79720"
     eth_privkey = "0x2a871d0798f97d79848a013d4936a73bf4cc922c825d33c1cf7073dff6d409c6"
-    sleep(3)
+    # Poll until Anvil accepts connections. Fail immediately if the process
+    # exits (for example a genesis failure), rather than waiting out the deadline.
+    deadline = time.monotonic() + 60
+    while time.monotonic() < deadline:
+        if p.poll() is not None:
+            raise RuntimeError(
+                f"Anvil exited before listening on port {port} (code {p.returncode})"
+            )
+        try:
+            with socket.create_connection(("127.0.0.1", port), timeout=1):
+                break
+        except OSError:
+            time.sleep(0.5)
+    else:
+        p.kill()
+        p.wait()
+        raise RuntimeError(f"Anvil did not start on port {port} within 60s")
     yield AnvilInstance(f"http://127.0.0.1:{port}", eth_address, eth_privkey)
     p.kill()
     p.wait()
diff --git a/tests/test_v4_examples.py b/tests/test_v4_examples.py
index 0d0320c..003e7fc 100644
--- a/tests/test_v4_examples.py
+++ b/tests/test_v4_examples.py
@@ -14,9 +14,10 @@
 
 import os
 import shutil
+import socket
 import subprocess
+import time
 from dataclasses import dataclass
-from time import sleep
 from typing import Generator
 
 import pytest
@@ -98,7 +99,23 @@ def anvil() -> Generator[AnvilInstance, None, None]:
     # Anvil test account #2 (1000 ETH pre-funded)
     eth_address = "0x3C44CdDdB6a900fa2b585dd299e03d12FA4293BC"
     eth_privkey = "0x5de4111afa1a4b94908f83103eb1f1706367c2e68ca870fc3fb9a804cdab365a"
-    sleep(3)
+    # Poll until Anvil accepts connections. Fail immediately if the process
+    # exits (for example a genesis failure), rather than waiting out the deadline.
+    deadline = time.monotonic() + 60
+    while time.monotonic() < deadline:
+        if p.poll() is not None:
+            raise RuntimeError(
+                f"Anvil exited before listening on port {port} (code {p.returncode})"
+            )
+        try:
+            with socket.create_connection(("127.0.0.1", port), timeout=1):
+                break
+        except OSError:
+            time.sleep(0.5)
+    else:
+        p.kill()
+        p.wait()
+        raise RuntimeError(f"Anvil did not start on port {port} within 60s")
     yield AnvilInstance(f"http://127.0.0.1:{port}", eth_address, eth_privkey)
     p.kill()
     p.wait()