diff --git a/share/man/man4/snp.4 b/share/man/man4/snp.4
--- a/share/man/man4/snp.4
+++ b/share/man/man4/snp.4
@@ -1,7 +1,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd November 5, 2008
+.Dd September 24, 2022
 .Dt SNP 4
 .Os
 .Sh NAME
@@ -58,8 +58,6 @@
 in a read buffer.
 Special values defined are:
 .Bl -tag -width ".Dv SNP_TTYCLOSE"
-.It Dv SNP_OFLOW
-device overflow occurred, device detached.
 .It Dv SNP_TTYCLOSE
 tty not attached.
 .It Dv SNP_DETACH
@@ -89,11 +87,3 @@
 .Nm
 were based on code written by
 .An Ugen J.S. Antsilevich Aq Mt ugen@NetVision.net.il .
-.Sh BUGS
-This version of
-.Nm
-does not return proper error codes when calling
-.Dv FIONREAD .
-It also does not allow
-.Dv SNPSTTY
-to detach itself from the TTY.
diff --git a/sys/dev/snp/snp.c b/sys/dev/snp/snp.c
--- a/sys/dev/snp/snp.c
+++ b/sys/dev/snp/snp.c
@@ -125,6 +125,7 @@
 		tty_lock(tp);
 		ttyoutq_free(&ss->snp_outq);
 		ttyhook_unregister(tp);
+		ss->snp_tty = NULL;
 	}
 
 	cv_destroy(&ss->snp_outwait);
@@ -252,9 +253,19 @@
 	case SNPSTTY:
 		/* Bind TTY to snoop instance. */
 		SNP_LOCK();
-		if (ss->snp_tty != NULL) {
+		tp = ss->snp_tty;
+		if (tp != NULL) {
+			if (*(int *)data == -1) {
+				tty_lock(tp);
+				ss->snp_tty = NULL;
+				ttyoutq_free(&ss->snp_outq);
+				ttyhook_unregister(tp);
+				error = 0;
+			} else {
+				error = EBUSY;
+			}
 			SNP_UNLOCK();
-			return (EBUSY);
+			return (error);
 		}
 		/*
 		 * XXXRW / XXXJA: no capability check here.
@@ -289,10 +300,13 @@
 		tp = ss->snp_tty;
 		if (tp != NULL) {
 			tty_lock(tp);
-			*(int *)data = ttyoutq_bytesused(&ss->snp_outq);
+			if (tty_gone(tp))
+				*(int *)data = SNP_TTYCLOSE;
+			else
+				*(int *)data = ttyoutq_bytesused(&ss->snp_outq);
 			tty_unlock(tp);
 		} else {
-			*(int *)data = 0;
+			*(int *)data = SNP_DETACH;
 		}
 		return (0);
 	default: