diff --git a/CHANGES/12136.bugfix.rst b/CHANGES/12136.bugfix.rst
new file mode 100644
index 00000000000..14ad7edf326
--- /dev/null
+++ b/CHANGES/12136.bugfix.rst
@@ -0,0 +1,2 @@
+``ClientConnectorCertificateError.os_error`` no longer raises :exc:`AttributeError`
+-- by :user:`themylogin`.
diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index 7c5613648ca..487691f688f 100644
--- a/CONTRIBUTORS.txt
+++ b/CONTRIBUTORS.txt
@@ -392,6 +392,7 @@ Vladimir Kamarzin
 Vladimir Kozlovski
 Vladimir Rutsky
 Vladimir Shulyak
+Vladimir Vinogradenko
 Vladimir Zakharov
 Vladyslav Bohaichuk
 Vladyslav Bondar
diff --git a/aiohttp/client_exceptions.py b/aiohttp/client_exceptions.py
index af83a42705e..3b66c7fdcd2 100644
--- a/aiohttp/client_exceptions.py
+++ b/aiohttp/client_exceptions.py
@@ -342,10 +342,21 @@ class ClientConnectorSSLError(*ssl_error_bases):  # type: ignore[misc]
 class ClientConnectorCertificateError(*cert_errors_bases):  # type: ignore[misc]
     """Response certificate error."""
 
+    _conn_key: ConnectionKey
+
     def __init__(
-        self, connection_key: ConnectionKey, certificate_error: Exception
+        # TODO: If we require ssl in future, this can become ssl.CertificateError
+        self,
+        connection_key: ConnectionKey,
+        certificate_error: Exception,
     ) -> None:
-        self._conn_key = connection_key
+        if isinstance(certificate_error, cert_errors + (OSError,)):
+            # ssl.CertificateError has errno and strerror, so we should be fine
+            os_error = certificate_error
+        else:
+            os_error = OSError()
+
+        super().__init__(connection_key, os_error)
         self._certificate_error = certificate_error
         self.args = (connection_key, certificate_error)
 
diff --git a/tests/test_client_exceptions.py b/tests/test_client_exceptions.py
index ed87b6d50f1..a7bf4db05ef 100644
--- a/tests/test_client_exceptions.py
+++ b/tests/test_client_exceptions.py
@@ -201,6 +201,15 @@ def test_str(self) -> None:
             " [Exception: ('Bad certificate',)]"
         )
 
+    def test_oserror(self) -> None:
+        certificate_error = OSError(1, "Bad certificate")
+        err = client.ClientConnectorCertificateError(
+            connection_key=self.connection_key, certificate_error=certificate_error
+        )
+        assert err.os_error == certificate_error
+        assert err.errno == 1
+        assert err.strerror == "Bad certificate"
+
 
 class TestServerDisconnectedError:
     def test_ctor(self) -> None: