diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8fca419d..47a6e4bc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,11 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ## [Unreleased]
 
+### Added
+
+- Add `avoid_efx_ioctl` option to avoid sfc proprietary ioctl(). (SWPTP-1535)
+  - This prevents setting of the sync flags optionally used by Onload.
+
 ### Fixed
 
 - Issue SWPTP-1506
diff --git a/src/sfptpd_clock.c b/src/sfptpd_clock.c
index 29f2c450..6fd66723 100644
--- a/src/sfptpd_clock.c
+++ b/src/sfptpd_clock.c
@@ -801,7 +801,7 @@ static int renew_clock(struct sfptpd_clock *clock)
 		/* Set the primary interface for the clock and get the PHC
 		 * supported flag and device index. */
 		clock->u.nic.primary_if = primary;
-		clock->u.nic.supports_sync_status_reporting = true;
+		clock->u.nic.supports_sync_status_reporting = !clock->cfg_avoid_efx;
 		clock->u.nic.device_idx = phc_idx;
 		clock->u.nic.supports_efx = supports_efx;
 
@@ -2219,8 +2219,7 @@ int sfptpd_clock_set_sync_status(struct sfptpd_clock *clock, bool in_sync,
 		goto finish;
 	}
 
-	/* Update the sync status via a private IOCTL.
-	   Ignore clock->cfg_avoid_efx because there is no alternative mechanism. */
+	/* Update the sync status via a private IOCTL unless inhibited. */
 	memset(&sfc_req, 0, sizeof(sfc_req));
 	sfc_req.cmd = EFX_TS_SET_SYNC_STATUS;
 	sfc_req.u.ts_set_sync_status.in_sync = in_sync? 1: 0;
diff --git a/src/sfptpd_general_config.c b/src/sfptpd_general_config.c
index a1721a3e..af5f7df4 100644
--- a/src/sfptpd_general_config.c
+++ b/src/sfptpd_general_config.c
@@ -257,12 +257,12 @@ static const sfptpd_config_option_t config_general_options[] =
 		parse_assume_one_phc_per_nic,
 		.dfl = SFPTPD_CONFIG_DFL_BOOL(SFPTPD_DEFAULT_ASSUME_ONE_PHC_PER_NIC)},
 	{"avoid_efx_ioctl", "<off | on>",
-		"Specify whether to avoid private SIOCEFX ioctl for Solarflare "
-		"adapters where possible",
+		"Specify whether to avoid private SIOCEFX ioctl for Solarflare adapters. "
+		"This prevents use of the sync flag via Onload",
 		1, SFPTPD_CONFIG_SCOPE_GLOBAL,
 		parse_avoid_efx_ioctl,
 		.dfl = SFPTPD_CONFIG_DFL_BOOL(false),
-		.hidden = true},
+		},
 	{"phc_diff_methods", "<sys-offset-precise | efx | pps | sys-offset-ext | sys-offset | read-time>*",
 		"Define the list of PHC diff methods used",
 		~1, SFPTPD_CONFIG_SCOPE_GLOBAL,