diff --git a/sys/fs/fuse/fuse_device.c b/sys/fs/fuse/fuse_device.c
--- a/sys/fs/fuse/fuse_device.c
+++ b/sys/fs/fuse/fuse_device.c
@@ -82,6 +82,8 @@
 #include <sys/sysctl.h>
 #include <sys/poll.h>
 #include <sys/selinfo.h>
+#define EXTERR_CATEGORY EXTERR_CAT_FUSE
+#include <sys/exterrvar.h>
 
 #include "fuse.h"
 #include "fuse_internal.h"
@@ -193,6 +195,7 @@
 		kn->kn_fop = &fuse_device_wfiltops;
 		error = 0;
 	} else if (error == 0) {
+		SET_ERROR0(EINVAL, "Invalid kevent filter");
 		error = EINVAL;
 		kn->kn_data = error;
 	}
@@ -319,6 +322,7 @@
 			"we know early on that reader should be kicked so we "
 			"don't wait for news");
 		fuse_lck_mtx_unlock(data->ms_mtx);
+		SET_ERROR0(ENODEV, "This FUSE session is about to be closed");
 		return (ENODEV);
 	}
 	if (!(tick = fuse_ms_pop(data))) {
@@ -331,7 +335,11 @@
 			err = msleep(data, &data->ms_mtx, PCATCH, "fu_msg", 0);
 			if (err != 0) {
 				fuse_lck_mtx_unlock(data->ms_mtx);
-				return (fdata_get_dead(data) ? ENODEV : err);
+				if (fdata_get_dead(data)) {
+					SET_ERROR0(ENODEV, "This FUSE session is about to be closed");
+					return (ENODEV);
+				}
+				return (err);
 			}
 			tick = fuse_ms_pop(data);
 		}
@@ -361,6 +369,7 @@
 			FUSE_ASSERT_MS_DONE(tick);
 			fuse_ticket_drop(tick);
 		}
+		SET_ERROR0(ENODEV, "This FUSE session is about to be closed");
 		return (ENODEV);	/* This should make the daemon get off
 					 * of us */
 	}
@@ -385,6 +394,7 @@
 		fdata_set_dead(data);
 		SDT_PROBE2(fusefs, , device, trace, 2,
 		    "daemon is stupid, kick it off...");
+		SET_ERROR0(ENODEV, "Partial read attempted");
 		err = ENODEV;
 	} else {
 		err = uiomove(buf, buflen, uio);
@@ -400,14 +410,17 @@
 fuse_ohead_audit(struct fuse_out_header *ohead, struct uio *uio)
 {
 	if (uio->uio_resid + sizeof(struct fuse_out_header) != ohead->len) {
-		SDT_PROBE2(fusefs, , device, trace, 1,
-			"Format error: body size "
-			"differs from size claimed by header");
+		static const char* exterr = "Format error: body size "
+			"differs from size claimed by header";
+		SDT_PROBE2(fusefs, , device, trace, 1, exterr);
+		SET_ERROR0(EINVAL, exterr);
 		return (EINVAL);
 	}
 	if (uio->uio_resid && ohead->unique != 0 && ohead->error) {
-		SDT_PROBE2(fusefs, , device, trace, 1, 
-			"Format error: non zero error but message had a body");
+		static const char* exterr = "Format error: non zero "
+			"error, but message has a body";
+		SDT_PROBE2(fusefs, , device, trace, 1, exterr);
+		SET_ERROR0(EINVAL, exterr);
 		return (EINVAL);
 	}
 
@@ -441,9 +454,10 @@
 		return (err);
 
 	if (uio->uio_resid < sizeof(struct fuse_out_header)) {
-		SDT_PROBE2(fusefs, , device, trace, 1,
-			"fuse_device_write got less than a header!");
+		static const char* exterr = "fuse_device_write got less than a header!";
+		SDT_PROBE2(fusefs, , device, trace, 1, exterr);
 		fdata_set_dead(data);
+		SET_ERROR0(EINVAL, exterr);
 		return (EINVAL);
 	}
 	if ((err = uiomove(&ohead, sizeof(struct fuse_out_header), uio)) != 0)
@@ -451,8 +465,10 @@
 
 	if (data->linux_errnos != 0 && ohead.error != 0) {
 		err = -ohead.error;
-		if (err < 0 || err >= nitems(linux_to_bsd_errtbl))
+		if (err < 0 || err >= nitems(linux_to_bsd_errtbl)) {
+			SET_ERROR0(EINVAL, "Unknown Linux errno");
 			return (EINVAL);
+		}
 
 		/* '-', because it will get flipped again below */
 		ohead.error = -linux_to_bsd_errtbl[err];
@@ -520,6 +536,7 @@
 				memcpy(&tick->tk_aw_ohead, &ohead,
 					sizeof(ohead));
 				tick->tk_aw_handler(tick, uio);
+				SET_ERROR0(EINVAL, "Unknown Linux errno");
 				err = EINVAL;
 			} else {
 				memcpy(&tick->tk_aw_ohead, &ohead,
@@ -570,6 +587,7 @@
 			/* Unimplemented.  See comments in fuse_vnops */
 		default:
 			/* Not implemented */
+			SET_ERROR0(ENOSYS, "Unknown FUSE error in out header");
 			err = ENOSYS;
 		}
 		vfs_unbusy(mp);
@@ -589,6 +607,7 @@
 			 */
 			err = 0;
 		} else {
+			SET_ERROR0(ENOSYS, "FUSE ticket is missing");
 			err = EINVAL;
 		}
 	}
diff --git a/sys/fs/fuse/fuse_vfsops.c b/sys/fs/fuse/fuse_vfsops.c
--- a/sys/fs/fuse/fuse_vfsops.c
+++ b/sys/fs/fuse/fuse_vfsops.c
@@ -81,6 +81,8 @@
 #include <sys/mount.h>
 #include <sys/sysctl.h>
 #include <sys/fcntl.h>
+#define EXTERR_CATEGORY EXTERR_CAT_FUSE
+#include <sys/exterrvar.h>
 
 #include "fuse.h"
 #include "fuse_node.h"
@@ -271,8 +273,10 @@
 	struct vnode *nvp;
 	int error;
 
-	if (!(fuse_get_mpdata(mp)->dataflags & FSESS_EXPORT_SUPPORT))
+	if (!(fuse_get_mpdata(mp)->dataflags & FSESS_EXPORT_SUPPORT)) {
+		SET_ERROR0(EOPNOTSUPP, "NFS-style lookups are not supported");
 		return EOPNOTSUPP;
+	}
 
 	error = VFS_VGET(mp, ffhp->nid, LK_EXCLUSIVE, &nvp);
 	if (error) {
@@ -320,12 +324,16 @@
 	/* Get the new options passed to mount */
 	opts = mp->mnt_optnew;
 
-	if (!opts)
+	if (!opts) {
+		SET_ERROR0(EINVAL, "Mount options were not supplied");
 		return EINVAL;
+	}
 
 	/* `fspath' contains the mount point (eg. /mnt/fuse/sshfs); REQUIRED */
-	if (!vfs_getopts(opts, "fspath", &err))
+	if (!vfs_getopts(opts, "fspath", &err)) {
+		SET_ERROR0(err, "Mount options are missing 'fspath'");
 		return err;
+	}
 
 	/*
 	 * With the help of underscored options the mount program
@@ -357,12 +365,16 @@
 
 	/* `from' contains the device name (eg. /dev/fuse0); REQUIRED */
 	fspec = vfs_getopts(opts, "from", &err);
-	if (!fspec)
+	if (!fspec) {
+		SET_ERROR0(err, "Mount options are missing 'from'");
 		return err;
+	}
 
 	/* `fd' contains the filedescriptor for this session; REQUIRED */
-	if (vfs_scanopt(opts, "fd", "%d", &fd) != 1)
+	if (vfs_scanopt(opts, "fd", "%d", &fd) != 1) {
+		SET_ERROR0(EINVAL, "Mount options are missing 'fd'");
 		return EINVAL;
+	}
 
 	err = fuse_getdevice(fspec, td, &fdev);
 	if (err != 0)
@@ -398,11 +410,15 @@
 	/* Sanity + permission checks */
 	if (!data->daemoncred)
 		panic("fuse daemon found, but identity unknown");
-	if (mntopts & FSESS_DAEMON_CAN_SPY)
+	if (mntopts & FSESS_DAEMON_CAN_SPY) {
 		err = priv_check(td, PRIV_VFS_FUSE_ALLOWOTHER);
-	if (err == 0 && td->td_ucred->cr_uid != data->daemoncred->cr_uid)
+		SET_ERROR0(err, "FUSE daemon requires privileges due to 'allow_other' option");
+	}
+	if (err == 0 && td->td_ucred->cr_uid != data->daemoncred->cr_uid) {
 		/* are we allowed to do the first mount? */
 		err = priv_check(td, PRIV_VFS_FUSE_MOUNT_NONUSER);
+		SET_ERROR0(err, "Mounting as an user that is different from FUSE daemon's one requires privileges");
+	}
 	if (err) {
 		FUSE_UNLOCK();
 		goto out;
@@ -549,6 +565,7 @@
 		 * nullfs mount of a fusefs file system.
 		 */
 		SDT_PROBE1(fusefs, , vfsops, invalidate_without_export, mp);
+		SET_ERROR0(EOPNOTSUPP, "NFS-style lookups are not supported");
 		return (EOPNOTSUPP);
 	}
 
diff --git a/sys/sys/exterr_cat.h b/sys/sys/exterr_cat.h
--- a/sys/sys/exterr_cat.h
+++ b/sys/sys/exterr_cat.h
@@ -15,6 +15,7 @@
 #define	EXTERR_CAT_FILEDESC	2
 #define	EXTERR_KTRACE		3	/* To allow inclusion of this
 					   file into kern_ktrace.c */
+#define	EXTERR_CAT_FUSE		4
 
 #endif