diff --git a/eglot-tests.el b/eglot-tests.el
index c6d7ee2f..be5dbe8f 100644
--- a/eglot-tests.el
+++ b/eglot-tests.el
@@ -401,6 +401,31 @@ Pass TIMEOUT to `eglot--with-timeout'."
                    (and (string= (eglot--path-to-uri "Cargo.toml") uri)
                         (= type 3))))))))))
 
+(ert-deftest ccls-initialization-options ()
+  "Test ccls initialization."
+  (skip-unless (executable-find "ccls"))
+  (eglot--with-fixture
+      '(("project/main/" . (("main.cc" . "")))
+        ("project/.git/" . nil))
+      (let ((root (file-name-as-directory default-directory))
+            (eglot-ccls-initialization-options '((:index . (:threads 1)))))
+      (with-current-buffer
+        (eglot--find-file-noselect "project/main/main.cc")
+        (eglot--sniffing (:client-requests c-reqs)
+          (should (eglot--tests-connect 10))
+          (eglot--wait-for (c-reqs 10)
+              (&key _id method params &allow-other-keys)
+            (when (string= method "initialize")
+              (let* ((initialization-options (plist-get params :initializationOptions))
+                     (indexing-threads-opts
+                      (plist-get
+                       (plist-get initialization-options :index) :threads)))
+                (should (equal
+                         indexing-threads-opts
+                         (plist-get
+                          (plist-get
+                           eglot-ccls-initialization-options :index) :threads)))))))))))
+
 (ert-deftest basic-diagnostics ()
   "Test basic diagnostics."
   (skip-unless (executable-find "pyls"))
diff --git a/eglot.el b/eglot.el
index c752322b..83e12eca 100644
--- a/eglot.el
+++ b/eglot.el
@@ -102,7 +102,7 @@
                                 (sh-mode . ("bash-language-server" "start"))
 				                        (php-mode . ("php" "vendor/felixfbecker/\
 language-server/bin/php-language-server.php"))
-                                ((c++-mode c-mode) . ("ccls"))
+                                ((c++-mode c-mode) . (eglot-ccls "ccls"))
                                 ((caml-mode tuareg-mode reason-mode)
                                  . ("ocaml-language-server" "--stdio"))
                                 (ruby-mode
@@ -2713,6 +2713,19 @@ If INTERACTIVE, prompt user for details."
   "Eclipse JDT breaks spec and replies with edits as arguments."
   (mapc #'eglot--apply-workspace-edit arguments))
 
+
+;;; ccls-specific
+;;;
+(defclass eglot-ccls (eglot-lsp-server) ()
+  :documentation "CCLS")
+
+(defvar-local eglot-ccls-initialization-options nil
+  "Property list of initialization options sent to CCLS on start.")
+
+(cl-defmethod eglot-initialization-options ((_server eglot-ccls))
+  "Passes through ccls initialization options."
+  eglot-ccls-initialization-options)
+
 (provide 'eglot)
 ;;; eglot.el ends here