diff --git a/Gemfile b/Gemfile
index 06eb956..6046b0c 100644
--- a/Gemfile
+++ b/Gemfile
@@ -2,7 +2,7 @@ source 'https://rubygems.org'
 
 gemspec
 
-gem "rdf", git: "git://github.com/ruby-rdf/rdf.git", branch: "develop"
+gem "rdf", git: "https://github.com/ruby-rdf/rdf", branch: "develop"
 
 group :debug do
   gem "byebug", platform: :mri
diff --git a/lib/sxp/reader/common_lisp.rb b/lib/sxp/reader/common_lisp.rb
index 44b6203..7ca59e9 100644
--- a/lib/sxp/reader/common_lisp.rb
+++ b/lib/sxp/reader/common_lisp.rb
@@ -7,7 +7,7 @@ module SXP; class Reader
   #
   # @see https:/www.cs.cmu.edu/Groups/AI/html/cltl/clm/node14.html
   class CommonLisp < Basic
-    OPTIONS         = {nil: nil, t: true, quote: :quote, function: :function}
+    OPTIONS         = {nil: false, t: true, quote: :quote, function: :function}
 
     DECIMAL         = /^[+-]?(\d*)?\.\d*$/
     INTEGER_BASE_2  = /^[+-]?[01]+$/
@@ -35,7 +35,7 @@ class CommonLisp < Basic
     #
     # @param  [IO, StringIO, String]   input
     # @param  [Hash{Symbol => Object}] options
-    # @option options [Object]         :nil      (nil)
+    # @option options [Object]         :nil      (false)
     # @option options [Object]         :t        (true)
     # @option options [Object]         :quote    (:quote)
     # @option options [Object]         :function (:function)
@@ -69,6 +69,21 @@ def read_sharp
       end
     end
 
+    ##
+    # Based on Basic#read_atom, but adds 't' and 'nil' atoms.
+    # @return [Object]
+    def read_atom
+      case buffer = read_literal
+        when '.'      then buffer.to_sym
+        when RATIONAL then Rational($1.to_i, $2.to_i)
+        when DECIMAL  then Float(buffer) # FIXME?
+        when INTEGER  then Integer(buffer)
+        when /^t$/i   then true
+        when /^nil$/i then nil
+        else buffer.to_sym
+      end
+    end
+
     ##
     # @return [Symbol]
     def read_symbol(delimiter = nil)
diff --git a/spec/common_lisp_spec.rb b/spec/common_lisp_spec.rb
index b9526c1..4413ad2 100644
--- a/spec/common_lisp_spec.rb
+++ b/spec/common_lisp_spec.rb
@@ -76,6 +76,22 @@
     end
   end
 
+  context "when reading atoms" do
+    {
+      't' => true,
+      'T' => true,
+      'nil' => nil,
+      'NIL' => nil,
+      '1/2' => Rational(1, 2),
+      '1.0' => Float(1.0),
+      "10" => Integer(10),
+    }.each_pair do |input, output|
+      it "reads #{input} as an atom" do
+        expect(read(input)).to eq output
+      end
+    end
+  end
+
   context "when reading lists" do
     it "reads `()` as an empty list" do
       expect(read(%q(()))).to eq [] # FIXME