diff --git a/lib/oga/xpath/compiler.rb b/lib/oga/xpath/compiler.rb
index f7657d2..6de912c 100644
--- a/lib/oga/xpath/compiler.rb
+++ b/lib/oga/xpath/compiler.rb
@@ -927,7 +927,7 @@ module Oga
         call_arg.assign(arg_ast).followed_by do
           converted = conversion.to_boolean(call_arg).not
 
-          block_given? ? converted.if_false { yield } : converted
+          block_given? ? converted.if_true { yield } : converted
         end
       end
 
diff --git a/spec/oga/xpath/compiler/calls/not_spec.rb b/spec/oga/xpath/compiler/calls/not_spec.rb
index b37f8b6..367411b 100644
--- a/spec/oga/xpath/compiler/calls/not_spec.rb
+++ b/spec/oga/xpath/compiler/calls/not_spec.rb
@@ -28,7 +28,8 @@ describe Oga::XPath::Compiler do
 
     describe 'in a predicate' do
       it 'returns a NodeSet containing all matching nodes ' do
-        evaluate_xpath(@document, 'root[not(node())]').should == node_set(@root)
+        evaluate_xpath(@document, 'root[not(comment())]')
+          .should == node_set(@root)
       end
     end
   end