diff --git a/sys/dev/mmc/mmc.c b/sys/dev/mmc/mmc.c
index eb762562c4b6..a65ff41827b6 100644
--- a/sys/dev/mmc/mmc.c
+++ b/sys/dev/mmc/mmc.c
@@ -118,7 +118,7 @@ struct mmc_ivars {
 static SYSCTL_NODE(_hw, OID_AUTO, mmc, CTLFLAG_RD, NULL, "mmc driver");
 
 static int mmc_debug;
-SYSCTL_INT(_hw_mmc, OID_AUTO, debug, CTLFLAG_RW, &mmc_debug, 0, "Debug level");
+SYSCTL_INT(_hw_mmc, OID_AUTO, debug, CTLFLAG_RWTUN, &mmc_debug, 0, "Debug level");
 
 /* bus entry points */
 static int mmc_acquire_bus(device_t busdev, device_t dev);