diff --git a/lib/linguist/heuristics.rb b/lib/linguist/heuristics.rb
index 0d0b8338..48b64d0c 100644
--- a/lib/linguist/heuristics.rb
+++ b/lib/linguist/heuristics.rb
@@ -165,5 +165,13 @@ module Linguist
         Language["text"]
       end
     end
+
+    disambiguate "Common Lisp", "NewLisp" do |data|
+      if /^\s*\((defun|defactor|in-package|defpackage) /.match(data)
+        Language["Common Lisp"]
+      elsif /^\s*\(define /.match(data)
+        Language["NewLisp"]
+      end
+    end
   end
 end
diff --git a/test/test_heuristics.rb b/test/test_heuristics.rb
index 4b208770..195fb7c8 100644
--- a/test/test_heuristics.rb
+++ b/test/test_heuristics.rb
@@ -126,6 +126,13 @@ class TestHeuristcs < Test::Unit::TestCase
     })
   end
 
+  def test_lsp_by_heuristics
+    assert_heuristics({
+      "Common Lisp" => all_fixtures("Common Lisp"),
+      "NewLisp" => all_fixtures("NewLisp")
+    })
+  end
+
   def assert_heuristics(hash)
     candidates = hash.keys.map { |l| Language[l] }