diff --git a/Rakefile b/Rakefile
index d3dc46b..f9f53f5 100644
--- a/Rakefile
+++ b/Rakefile
@@ -6,7 +6,7 @@ require 'rake/extensiontask'
 
 spec = Gem::Specification.load('digest-blake2b.gemspec')
 
-Rake::ExtensionTask.new('digest/blake2b', spec) do |ext|
+Rake::ExtensionTask.new("digest/blake2b/#{Digest::Blake2b::IMPL}", spec) do |ext|
   ext.source_pattern = '*.{c,h}'
   ext.ext_dir = "ext/digest/blake2b/#{Digest::Blake2b::IMPL}"
 end