diff --git a/modules/caddytls/cf.go b/modules/caddytls/cf.go
deleted file mode 100644
index e61a59c09e1a..000000000000
--- a/modules/caddytls/cf.go
+++ /dev/null
@@ -1,24 +0,0 @@
-//go:build cfgo
-
-package caddytls
-
-// This file adds support for X25519Kyber768Draft00, a post-quantum
-// key agreement that is currently being rolled out by Chrome [1]
-// and Cloudflare [2,3]. For more context, see the PR [4].
-//
-// [1] https://blog.chromium.org/2023/08/protecting-chrome-traffic-with-hybrid.html
-// [2] https://blog.cloudflare.com/post-quantum-for-all/
-// [3] https://blog.cloudflare.com/post-quantum-to-origins/
-// [4] https://github.com/caddyserver/caddy/pull/5852
-
-import (
-	"crypto/tls"
-)
-
-func init() {
-	SupportedCurves["X25519Kyber768Draft00"] = tls.X25519Kyber768Draft00
-	defaultCurves = append(
-		[]tls.CurveID{tls.X25519Kyber768Draft00},
-		defaultCurves...,
-	)
-}
diff --git a/modules/caddytls/connpolicy.go b/modules/caddytls/connpolicy.go
index 4ec0e673a774..b54f27294b72 100644
--- a/modules/caddytls/connpolicy.go
+++ b/modules/caddytls/connpolicy.go
@@ -841,7 +841,15 @@ func setDefaultTLSParams(cfg *tls.Config) {
 	cfg.CipherSuites = append([]uint16{tls.TLS_FALLBACK_SCSV}, cfg.CipherSuites...)
 
 	if len(cfg.CurvePreferences) == 0 {
-		cfg.CurvePreferences = defaultCurves
+		// We would want to write
+		//
+		//	cfg.CurvePreferences = defaultCurves
+		//
+		// but that would disable the post-quantum key agreement X25519Kyber768
+		// supported in Go 1.23, for which the CurveID is not exported.
+		// Instead, we'll set CurvePreferences to nil, which will enable PQC.
+		// See https://github.com/caddyserver/caddy/issues/6540.
+		cfg.CurvePreferences = nil
 	}
 
 	if cfg.MinVersion == 0 {