diff --git a/doc/api/errors.md b/doc/api/errors.md
index 642d2445e53931..c0952792727e53 100644
--- a/doc/api/errors.md
+++ b/doc/api/errors.md
@@ -861,8 +861,9 @@ size is reached when the context is created.
 
 ### `ERR_CRYPTO_CUSTOM_ENGINE_NOT_SUPPORTED`
 
-A client certificate engine was requested that is not supported by the version
-of OpenSSL being used.
+An OpenSSL engine was requested (for example, through the `clientCertEngine` or
+`privateKeyEngine` TLS options) that is not supported by the version of OpenSSL
+being used, likely due to the compile-time flag `OPENSSL_NO_ENGINE`.
 
 <a id="ERR_CRYPTO_ECDH_INVALID_FORMAT"></a>