diff --git a/lsp-completion.el b/lsp-completion.el
index f29fe913b91..fda4ffc240b 100644
--- a/lsp-completion.el
+++ b/lsp-completion.el
@@ -355,7 +355,7 @@ The MARKERS and PREFIX value will be attached to each candidate."
          ;; `lsp-completion-start-point' above might be from cached/previous completion and
          ;; pointing to a very distant point, which results in `prefix' being way too long.
          ;; So let's consider only the first line.
-         (prefix (car (string-lines prefix)))
+         (prefix (car (s-lines prefix)))
          (prefix-len (length prefix))
          (prefix-pos 0)
          (label (downcase candidate))