diff --git a/lib/oga/xpath/lexer.rl b/lib/oga/xpath/lexer.rl
index 5cdf58e..c2e7064 100644
--- a/lib/oga/xpath/lexer.rl
+++ b/lib/oga/xpath/lexer.rl
@@ -178,8 +178,8 @@ module Oga
         # instead lexes them separately so that we can convert the values to
         # the corresponding Ruby types (Fixnum and Float).
 
-        integer = digit+;
-        float   = digit+ ('.' digit+)*;
+        integer = ('-' | '+')* digit+;
+        float   = ('-' | '+')* digit+ ('.' digit+)*;
 
         action emit_integer {
           value = slice_input(ts, te).to_i
diff --git a/spec/oga/xpath/lexer/floats_spec.rb b/spec/oga/xpath/lexer/floats_spec.rb
new file mode 100644
index 0000000..3ff0999
--- /dev/null
+++ b/spec/oga/xpath/lexer/floats_spec.rb
@@ -0,0 +1,13 @@
+require 'spec_helper'
+
+describe Oga::XPath::Lexer do
+  context 'floats' do
+    example 'lex a float' do
+      lex_xpath('10.0').should == [[:T_FLOAT, 10.0]]
+    end
+
+    example 'lex a negative float' do
+      lex_xpath('-10.0').should == [[:T_FLOAT, -10.0]]
+    end
+  end
+end
diff --git a/spec/oga/xpath/lexer/integers_spec.rb b/spec/oga/xpath/lexer/integers_spec.rb
new file mode 100644
index 0000000..9a6d8e0
--- /dev/null
+++ b/spec/oga/xpath/lexer/integers_spec.rb
@@ -0,0 +1,13 @@
+require 'spec_helper'
+
+describe Oga::XPath::Lexer do
+  context 'integers' do
+    example 'lex an integer' do
+      lex_xpath('10').should == [[:T_INT, 10]]
+    end
+
+    example 'lex a negative integer' do
+      lex_xpath('-10').should == [[:T_INT, -10]]
+    end
+  end
+end