diff --git a/eglot.el b/eglot.el
index 723ac3bc..4098c410 100644
--- a/eglot.el
+++ b/eglot.el
@@ -1952,10 +1952,11 @@ is not active."
        :company-prefix-length
        (save-excursion
          (when (car bounds) (goto-char (car bounds)))
-         (looking-back
-          (regexp-opt
-           (cl-coerce (cl-getf completion-capability :triggerCharacters) 'list))
-          (line-beginning-position)))
+         (when (listp completion-capability)
+           (looking-back
+            (regexp-opt
+             (cl-coerce (cl-getf completion-capability :triggerCharacters) 'list))
+            (line-beginning-position))))
        :exit-function
        (lambda (comp _status)
          (let ((comp (if (get-text-property 0 'eglot--lsp-completion comp)