diff --git a/shared/nm-glib-aux/nm-shared-utils.c b/shared/nm-glib-aux/nm-shared-utils.c
index a2e90273c5..48635df343 100644
--- a/shared/nm-glib-aux/nm-shared-utils.c
+++ b/shared/nm-glib-aux/nm-shared-utils.c
@@ -4966,7 +4966,12 @@ nm_str_buf_append_printf (NMStrBuf *strbuf,
 	nm_assert (l < G_MAXINT);
 
 	if ((gsize) l >= available) {
-		gsize l2 = ((gsize) l) + 1u;
+		gsize l2;
+
+		if (l == 0)
+			return;
+
+		l2 = ((gsize) l) + 1u;
 
 		nm_str_buf_maybe_expand (strbuf, l2, FALSE);