diff --git a/lib/sxp/reader/common_lisp.rb b/lib/sxp/reader/common_lisp.rb
index 824acbd..7ca59e9 100644
--- a/lib/sxp/reader/common_lisp.rb
+++ b/lib/sxp/reader/common_lisp.rb
@@ -79,7 +79,7 @@ def read_atom
         when DECIMAL  then Float(buffer) # FIXME?
         when INTEGER  then Integer(buffer)
         when /^t$/i   then true
-        when /^nil$/i then false
+        when /^nil$/i then nil
         else buffer.to_sym
       end
     end
diff --git a/spec/common_lisp_spec.rb b/spec/common_lisp_spec.rb
index 50d259e..4413ad2 100644
--- a/spec/common_lisp_spec.rb
+++ b/spec/common_lisp_spec.rb
@@ -80,8 +80,8 @@
     {
       't' => true,
       'T' => true,
-      'nil' => false,
-      'NIL' => false,
+      'nil' => nil,
+      'NIL' => nil,
       '1/2' => Rational(1, 2),
       '1.0' => Float(1.0),
       "10" => Integer(10),