diff --git a/src/zenrows/client.py b/src/zenrows/client.py
index 851ab4e..5f7bd2f 100644
--- a/src/zenrows/client.py
+++ b/src/zenrows/client.py
@@ -16,6 +16,7 @@
 import numbers
 import os
 import random
+import re
 import sys
 import time
 import warnings
@@ -42,6 +43,9 @@
 DEFAULT_RETRY_MAX_WAIT = 30.0
 DEFAULT_RETRY_BUDGET = 90.0
 
+# The API key as it appears in a request URL.
+_APIKEY_IN_URL = re.compile(r"apikey=[^&\s]*")
+
 # Clock for the retry budget; tests replace it.
 _monotonic = time.monotonic
 
@@ -125,6 +129,29 @@ def _failed_to_connect(error: requests.ConnectionError) -> bool:
     return isinstance(reason, ConnectTimeoutError)  # NewConnectionError is one too
 
 
+def _redact_apikey(error: BaseException) -> None:
+    """Replace the API key with REDACTED in the messages of `error` and of the
+    exceptions it wraps. A failed connection names the request URL, which
+    carries the key in `apikey`, so logging the error would log the key. The
+    exceptions stay the same objects."""
+    seen: set[int] = set()
+    pending = [error]
+    while pending:
+        exc = pending.pop()
+        if id(exc) in seen:
+            continue
+        seen.add(id(exc))
+        exc.args = tuple(
+            _APIKEY_IN_URL.sub("apikey=REDACTED", arg) if isinstance(arg, str) else arg
+            for arg in exc.args
+        )
+        pending += [
+            inner
+            for inner in (*exc.args, exc.__cause__, exc.__context__)
+            if isinstance(inner, BaseException)
+        ]
+
+
 def _from_target(status: int, params: dict) -> bool:
     """True when `status` may be the target site's own answer, which another
     try cannot change: any status with `original_status`, or one listed in
@@ -607,7 +634,7 @@ def _worker(
             final_headers["Connection"] = None
             final_headers.update(headers)
 
-        send = partial(
+        request = partial(
             self.requests_session.request,
             method,
             self.api_url,
@@ -616,6 +643,14 @@ def _worker(
             data=data,
             **kwargs,
         )
+
+        def send() -> requests.Response:
+            try:
+                return request()
+            except requests.RequestException as error:
+                _redact_apikey(error)
+                raise
+
         if not self.retries or not _can_send_again(method, data, kwargs):
             return send()
         started = _monotonic()
diff --git a/tests/test_client.py b/tests/test_client.py
index fff8bde..70a11c3 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -1,5 +1,8 @@
+import socket
+import traceback
 from unittest import TestCase, mock
 
+import requests
 import urllib3
 from requests import Session
 
@@ -152,3 +155,19 @@ def test_put_with_data(self, mock_request):
                 "key2": "value2",
             },
         )
+
+    def test_a_connection_error_hides_the_api_key(self):
+        with socket.socket() as sock:
+            sock.bind(("127.0.0.1", 0))
+            closed = f"http://127.0.0.1:{sock.getsockname()[1]}/v1/"
+        for retries in (0, 1):
+            client = ZenRowsClient("secret+key/=", base_url=closed, retries=retries)
+            with (
+                mock.patch("time.sleep"),
+                self.assertRaises(requests.ConnectionError) as raised,
+            ):
+                client.get(url)
+
+            printed = "".join(traceback.format_exception(raised.exception))
+            self.assertIn("apikey=REDACTED", str(raised.exception))
+            self.assertNotIn("secret", printed)