diff --git a/src/fennel-ls.fnl b/src/fennel-ls.fnl
index f0a3b46..059d620 100644
--- a/src/fennel-ls.fnl
+++ b/src/fennel-ls.fnl
@@ -2,13 +2,17 @@
 (local dispatch (require :fennel-ls.dispatch))
 (local json-rpc (require :fennel-ls.json-rpc))
 (local files (require :fennel-ls.files))
+(local {: severity->string} (require :fennel-ls.message))
 
-(fn print-diagnostic [filename message ?range]
-  (print (: "%s:%s:%s: %s" :format filename
+(fn print-diagnostic [filename message ?range ?severity]
+  (print (: "%s:%s:%s: %s: %s" :format
+            filename
             ;; LSP line numbers are zero-indexed, but Emacs and Vim both use
             ;; 1-indexing for this.
             (+ (or (?. ?range :start :line) 0) 1)
-            (or (?. ?range :start :character) "?") message)))
+            (or (?. ?range :start :character) "?")
+            (or (. severity->string ?severity) "?")
+            message)))
 
 (fn initialize [server]
   (let [params {:id 1
@@ -31,9 +35,9 @@
     (each [_ filename (ipairs filenames)]
       (let [file (files.get-by-uri server (.. "file://" filename))]
         (lint.add-lint-diagnostics server file)
-        (each [_ {: message : range} (ipairs file.diagnostics)]
+        (each [_ {: message : range : severity} (ipairs file.diagnostics)]
           (set should-err? true)
-          (print-diagnostic filename message range))))
+          (print-diagnostic filename message range severity))))
     (when should-err?
       (os.exit 1))))
 
diff --git a/src/fennel-ls/message.fnl b/src/fennel-ls/message.fnl
index 40c99ce..72209e7 100644
--- a/src/fennel-ls/message.fnl
+++ b/src/fennel-ls/message.fnl
@@ -35,6 +35,14 @@ LSP json objects."
    :INFO 3
    :HINT 4})
 
+(local severity->string
+  ;; Transforming the `severity` table into
+  ;; `{severity-code printable-string ...}`
+  (collect [k v (pairs severity)]
+    v (case k
+        :WARN :warning
+        _ (string.lower k))))
+
 (λ create-error [code message ?id ?data]
   {:jsonrpc "2.0"
    :id ?id
@@ -106,4 +114,5 @@ LSP json objects."
  : range-and-uri
  : diagnostics
  : severity
+ : severity->string
  : show-message}
diff --git a/test/check.fnl b/test/check.fnl
index 1676ef9..273c674 100644
--- a/test/check.fnl
+++ b/test/check.fnl
@@ -10,7 +10,7 @@
     (let [output-file (io.popen (.. "./fennel-ls --lint "
                                     input-file-name)
                                 :r)]
-      (faith.= (.. input-file-name ":1:7: unused definition: x\n")
+      (faith.= (.. input-file-name ":1:7: warning: unused definition: x\n")
                (output-file:read :*a))
       (os.remove input-file-name))
     nil))