diff --git a/.gitignore b/.gitignore
index 7d9456f95..f8b315e20 100644
--- a/.gitignore
+++ b/.gitignore
@@ -12,3 +12,4 @@ clerk.iml
 public/girouette.css
 public/images/
 yarn.lock
+*~
diff --git a/deps.edn b/deps.edn
index f7b366101..c8589de89 100644
--- a/deps.edn
+++ b/deps.edn
@@ -43,8 +43,14 @@
 
            :build {:deps {io.github.clojure/tools.build {:git/tag "v0.6.1" :git/sha "515b334"}
                           io.github.slipset/deps-deploy {:git/sha "b4359c5d67ca002d9ed0c4b41b710d7e5a82e3bf"}
-                          io.github.nextjournal/cas {:git/url "git@github.com:nextjournal/cas"
+                          io.github.nextjournal/cas {:git/url "https://github.com/nextjournal/cas"
                                                      :git/sha "5e8079b720e347b9466db9c2282ce79a125a011c"}
                           rewrite-clj/rewrite-clj {:mvn/version "1.0.699-alpha"}
                           babashka/fs {:mvn/version "0.0.5"}}
-                   :ns-default build}}}
+                   :ns-default build}
+
+           :test {:extra-paths ["test"]
+                  :extra-deps {io.github.cognitect-labs/test-runner
+                               {:git/tag "v0.5.0" :git/sha "b3fd0d2"}}
+                  :main-opts ["-m" "cognitect.test-runner"]
+                  :exec-fn cognitect.test-runner.api/test}}}
diff --git a/src/nextjournal/clerk.clj b/src/nextjournal/clerk.clj
index 8ab28d4b5..027697885 100644
--- a/src/nextjournal/clerk.clj
+++ b/src/nextjournal/clerk.clj
@@ -175,11 +175,21 @@
       (webserver/show-error! e)
       (throw e))))
 
+(defn supported-file?
+  "Returns whether PATH points to a file that can be visualized."
+  [path]
+
+  ;; Notes
+  ;;
+  ;; 1. file names starting with .# are most likely Emacs lock files
+  ;; and should be ignored.
+  (->> path io/file .getName
+       (re-matches #"(?!\.#).+\.(md|clj|cljc)$")
+       some?))
+
 (defn file-event [{:keys [type path]}]
   (when (and (contains? #{:modify :create} type)
-             (or (str/ends-with? path ".md")
-                 (str/ends-with? path ".clj")
-                 (str/ends-with? path ".cljc")))
+             (supported-file? path))
     (binding [*ns* (find-ns 'user)]
       (let [rel-path (str/replace (str path) (str (fs/canonicalize ".") fs/file-separator) "")
             show-file? (or (not @!show-filter-fn)
diff --git a/test/nextjournal/clerk_test.clj b/test/nextjournal/clerk_test.clj
new file mode 100644
index 000000000..0cb961394
--- /dev/null
+++ b/test/nextjournal/clerk_test.clj
@@ -0,0 +1,10 @@
+(ns nextjournal.clerk-test
+  (:require [nextjournal.clerk :as c]
+            [clojure.test :as t]))
+
+(t/deftest supported-filenames
+  (t/is (= true (c/supported-file? "xyz/name.md")))
+  (t/is (= true (c/supported-file? "xyz/name.clj")))
+  (t/is (= true (c/supported-file? "xyz/name.cljc")))
+  (t/is (= false (c/supported-file? "xyz/.#name.cljc")))
+  )