diff --git a/url-mode.c b/url-mode.c
index 00d38d75..f04550f8 100644
--- a/url-mode.c
+++ b/url-mode.c
@@ -389,8 +389,11 @@ regex_detected(const struct terminal *term, enum url_action action,
     }
 
     /* Terminate the last line, if necessary */
-    if (vline->len > 0 && vline->utf8[vline->len - 1] != '\0')
+    if (vline_idx < ALEN(vlines) &&
+        vline->len > 0 && vline->utf8[vline->len - 1] != '\0')
+    {
         vline->utf8[vline->len++] = '\0';
+    }
 
     for (size_t i = 0; i < ALEN(vlines); i++) {
         const struct vline *v = &vlines[i];