diff --git a/cmd-find.c b/cmd-find.c
index f9621b53e..183e5525d 100644
--- a/cmd-find.c
+++ b/cmd-find.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: cmd-find.c,v 1.87 2026/07/17 12:42:51 nicm Exp $ */
+/* $OpenBSD: cmd-find.c,v 1.88 2026/09/07 12:05:12 nicm Exp $ */
 
 /*
  * Copyright (c) 2015 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -388,9 +388,11 @@ cmd_find_get_window_with_session(struct cmd_find_state *fs, const char *window)
 
 	/* Try as an offset. */
 	if (!exact && (window[0] == '+' || window[0] == '-')) {
-		if (window[1] != '\0')
-			n = strtonum(window + 1, 1, INT_MAX, NULL);
-		else
+		if (window[1] != '\0') {
+			n = strtonum(window + 1, 1, INT_MAX, &errstr);
+			if (errstr != NULL)
+				return (-1);
+		} else
 			n = 1;
 		s = fs->s;
 		if (fs->flags & CMD_FIND_WINDOW_INDEX) {
@@ -626,9 +628,11 @@ cmd_find_get_pane_with_window(struct cmd_find_state *fs, const char *pane)
 
 	/* Try as an offset. */
 	if (pane[0] == '+' || pane[0] == '-') {
-		if (pane[1] != '\0')
-			n = strtonum(pane + 1, 1, INT_MAX, NULL);
-		else
+		if (pane[1] != '\0') {
+			n = strtonum(pane + 1, 1, INT_MAX, &errstr);
+			if (errstr != NULL)
+				return (-1);
+		} else
 			n = 1;
 		wp = fs->w->active;
 		if (pane[0] == '+')
diff --git a/monitor.c b/monitor.c
index ff0c6e5ed..596e137a7 100644
--- a/monitor.c
+++ b/monitor.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: monitor.c,v 1.7 2026/07/27 19:15:58 nicm Exp $ */
+/* $OpenBSD: monitor.c,v 1.8 2026/09/07 10:15:25 nicm Exp $ */
 
 /*
  * Copyright (c) 2026 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -614,8 +614,10 @@ monitor_parse(const char *value, char **name, enum monitor_type *type, int *id,
 		*type = MONITOR_ALL_WINDOWS;
 	else if (sscanf(what, "@%d", id) == 1 && *id >= 0)
 		*type = MONITOR_WINDOW;
-	else
+	else if (*what == '\0')
 		*type = MONITOR_SESSION;
+	else
+		goto fail;
 	*name = xstrdup(copy);
 	*format = xstrdup(split);