diff --git a/sys/cam/mmc/mmc_sim.h b/sys/cam/mmc/mmc_sim.h
--- a/sys/cam/mmc/mmc_sim.h
+++ b/sys/cam/mmc/mmc_sim.h
@@ -33,6 +33,7 @@
 struct mmc_sim {
 	struct mmc_cam_sim_softc	*sc;
 	struct mtx			mtx;
+	char				name[64];
 	struct cam_devq			*devq;
 	struct cam_sim			*sim;
 	device_t			dev;
diff --git a/sys/cam/mmc/mmc_sim.c b/sys/cam/mmc/mmc_sim.c
--- a/sys/cam/mmc/mmc_sim.c
+++ b/sys/cam/mmc/mmc_sim.c
@@ -191,7 +191,6 @@
 int
 mmc_cam_sim_alloc(device_t dev, const char *name, struct mmc_sim *mmc_sim)
 {
-	char sim_name[64], mtx_name[64];
 
 	mmc_sim->dev = dev;
 
@@ -199,13 +198,11 @@
 		goto fail;
 	}
 
-	snprintf(sim_name, sizeof(sim_name), "%s_sim", name);
-	snprintf(mtx_name, sizeof(mtx_name), "%s_mtx", name);
-
-	mtx_init(&mmc_sim->mtx, sim_name, NULL, MTX_DEF);
+	snprintf(mmc_sim->name, sizeof(mmc_sim->name), "%s_sim", name);
+	mtx_init(&mmc_sim->mtx, mmc_sim->name, NULL, MTX_DEF);
 	mmc_sim->sim = cam_sim_alloc(mmc_cam_sim_default_action,
 	    mmc_cam_default_poll,
-	    name, mmc_sim, device_get_unit(dev),
+	    mmc_sim->name, mmc_sim, device_get_unit(dev),
 	    &mmc_sim->mtx, 1, 1, mmc_sim->devq);
 
 	if (mmc_sim->sim == NULL) {