diff --git a/lib/linguist/heuristics.rb b/lib/linguist/heuristics.rb
index 2002d51b..1caab36b 100644
--- a/lib/linguist/heuristics.rb
+++ b/lib/linguist/heuristics.rb
@@ -289,5 +289,13 @@ module Linguist
         Language["RenderScript"]
       end
     end
+
+    disambiguate "Common Lisp", "Lex" do |data|
+      if data.include?("(def(un|macro)\s")
+        Language["Common Lisp"]
+      elsif /^(%[%{}]xs|<.*>)/.match(data)
+        Language["Lex"]
+      end
+    end
   end
 end
diff --git a/lib/linguist/languages.yml b/lib/linguist/languages.yml
index d99180c4..35a1f133 100644
--- a/lib/linguist/languages.yml
+++ b/lib/linguist/languages.yml
@@ -601,6 +601,7 @@ Common Lisp:
   - .lisp
   - .asd
   - .cl
+  - .l
   - .lsp
   - .ny
   - .podsl